Microbially-mediated method for synthesis of non-oxide semiconductor nanoparticles

ABSTRACT

The invention is directed to a method for producing non-oxide semiconductor nanoparticles, the method comprising: (a) subjecting a combination of reaction components to conditions conducive to microbially-mediated formation of non-oxide semiconductor nanoparticles, wherein said combination of reaction components comprises i) anaerobic microbes, ii) a culture medium suitable for sustaining said anaerobic microbes, iii) a metal component comprising at least one type of metal ion, iv) a non-metal component comprising at least one non-metal selected from the group consisting of S, Se, Te, and As, and v) one or more electron donors that provide donatable electrons to said anaerobic microbes during consumption of the electron donor by said anaerobic microbes; and (b) isolating said non-oxide semiconductor nanoparticles, which contain at least one of said metal ions and at least one of said non-metals. The invention is also directed to non-oxide semiconductor nanoparticle compositions produced as above and having distinctive properties.

CROSS REFERENCE TO RELATED APPLICATION

This application is a continuation-in-part of copending application Ser.No. 12/364,638 filed Feb. 3, 2009.

This invention was made with government support under Contract NumberDE-AC05-00OR22725 between the United States Department of Energy andUT-Battelle, LLC. The United States government has certain rights inthis invention.

FIELD OF THE INVENTION

The present invention relates to the field of microbial synthesis ofinorganic materials, and more particularly, microbial synthesis ofnon-oxide semiconductor nanoparticles.

BACKGROUND OF THE INVENTION

Nanoparticles having metal non-oxide compositions (i.e., “semiconductor”or “quantum dot” nanoparticles) are increasingly being used in numerousemerging applications. Some of these applications include electronics(e.g., transistors and diode lasers), LED displays, photovoltaics (e.g.,solar cells), and medical imaging. Quantum dot nanoparticles are alsobeing investigated as powerful new computer processing elements (i.e.,qubits). Semiconductor nanoparticles often possess a metal chalcogenidecomposition, such as CdSe and ZnS.

As a consequence of its small size, the electron band structure of aquantum dot differs significantly from that of the bulk material. Inparticular, significantly more of the atoms in the quantum dot are on ornear the surface, in contrast to the bulk material in which most of theatoms are far enough removed from the surface so that a normal bandstructure predominates. Thus, the electronic and optical properties of aquantum dot are related to its size. In particular, photoluminescence issize dependent.

Several physical methods are known for synthesizing semiconductornanoparticles. Some of the physical techniques include advancedepitaxial, ion implantation, and lithographic techniques. The physicaltechniques are generally useful for producing minute amounts ofsemiconductor nanoparticles with well-defined (i.e., tailor-made, andtypically, uniform) morphological, electronic, magnetic, or photoniccharacteristics. The physical techniques are typically not useful forsynthesizing semiconductor nanoparticles in commercially significantquantities (e.g., grams or kilograms).

Several chemical processes are also known for the production ofsemiconductor nanoparticles. Some of these methods include arrestedprecipitation in solution, synthesis in structured media, hightemperature pyrolysis, and sonochemical methods. For example, cadmiumselenide can be synthesized by arrested precipitation in solution byreacting dialkylcadmium (i.e., R₂Cd) and trioctylphosphine selenide(TOPSe) precursors in a solvent at elevated temperatures, i.e.,

R₂Cd+TOPSe→CdSe+byproducts

High temperature pyrolysis of semiconductor nanoparticles generallyentails preparing an aerosol containing a mixture of volatile cadmiumand selenium precursors, and then subjecting the aerosol to hightemperatures (e.g., by carrying through a furnace) in the presence of aninert gas. Under these conditions, the precursors react to form thesemiconductor nanoparticles (e.g., CdSe) and byproducts.

Though the chemical processes described above are generally capable ofproducing semiconductor nanoparticles in more significant quantities,the processes are generally energy intensive (e.g., by generallyrequiring heating and a post-annealing step), and hence, costly.Accordingly, commercially significant amounts of the resultingnanoparticles tend to be prohibitively expensive. Furthermore, theseprocesses tend to be significantly limited with respect to control ofthe physical (e.g., size, shape, and crystalline form) and electronic orphotonic characteristics of the resulting nanoparticles.

The microbial synthesis of semiconductor nanoparticles is known. See,for example, P. R. Smith, et al., J. Chem. Soc., Faraday Trans., 94(9),1235-1241 (1998) and C. T. Dameron, et al., Nature, 338: 596-7, (1989).However, there are significant obstacles that prevent suchmicrobially-mediated methods from being commercially viable. Forexample, current microbial methods are generally limited to theproduction of semiconductor nanoparticles on a research scale, i.e., anamount sufficient for elucidation by analytical methods. In addition,current microbial processes generally produce semiconductornanoparticles adhered to cell membranes. Accordingly, numerousseparation and washing steps are generally needed.

Accordingly, there is a need in the art for a microbial method for thesynthesis of semiconductor nanoparticles capable of producingsemiconductor nanoparticles on a commercial (i.e., bulk) scale at anon-prohibitive cost. There is also a need for a microbial method ofsynthesis that provides substantially pure semiconductor nanoparticleproduct bereft of microbial matter, thereby reducing or eliminatingseparation and washing steps. There is also a particular need for such amicrobial method of synthesis whereby characteristics of thenanoparticles (e.g., particle size, morphology, electronic or photoniccharacteristics, dopant composition, and doping level) are moreprecisely or uniformly controlled.

SUMMARY OF THE INVENTION

In one aspect, the invention is directed to a microbially-mediatedmethod for the production of semiconductor nanoparticles. The methoddescribed herein can advantageously produce a variety of semiconductornanoparticle compositions on a commercially viable scale. In addition,the method can advantageously produce semiconductor nanoparticles of aparticular particle size, morphology, electronic or photoniccharacteristic, dopant composition, or doping level. In particularembodiments, the semiconductor nanoparticles described herein are usefulas photovoltaic materials, as used, for example, in solar cell devices.

In particular embodiments, the method includes: (a) subjecting acombination of reaction components to conditions conducive tomicrobially-mediated formation of non-oxide semiconductor nanoparticles,wherein the combination of reaction components includes i) anaerobicmicrobes (i.e., “microbes”), ii) a culture medium suitable forsustaining the anaerobic microbes, iii) a chalcophile metal component(i.e., “metals” or “metal component”) that includes at least one type ofmetal ion to be included in the nanoparticle composition, iv) anon-metal component that includes at least one non-metal selected fromS, Se, Te, and As, and v) at least one electron donor that providesdonatable electrons to the anaerobic microbes during consumption of theelectron donor by the anaerobic microbes; and (b) isolating thenon-oxide semiconductor nanoparticles, which include at least one of themetal ions and at least one of the non-metals. In particularembodiments, steps (a) and (b) are performed as a single step process.

In a particular set of embodiments, the nanoparticles produced by themethodology described above have a CIGs-type composition according tothe general formula Cu(In_(x)Ga_(1-x))X₂, wherein x is an integral ornon-integral numerical value greater than 0 and less than or equal to 1,and X represents at least one non-metal selected from S, Se, and Te. Aparticular method considered herein for preparing the CIGs-typenanoparticles, in accordance with the above methodology, includes: (a)subjecting a combination of reaction components to conditions conduciveto microbially-mediated formation of the nanoparticles, wherein thecombination of reaction components includes i) anaerobic microbes, ii) aculture medium suitable for sustaining the anaerobic microbes, iii) ametal component that includes Cu ions and at least one type of metal ionselected from In and Ga, iv) a non-metal component that includes atleast one non-metal selected from S, Se, Te, and As, and v) one or moreelectron donors that provide donatable electrons to the anaerobicmicrobes during consumption of the electron donor by the anaerobicmicrobes; and (b) isolating the nanoparticles.

In another particular set of embodiments, the nanoparticles produced bythe methodology described above have a kesterite-type compositionaccording to the general formula M₃SnX₄, wherein M represents at leastone chalcophile metal and X represents at least one non-metal selectedfrom S, Se, and Te. A particular method considered herein for preparingthe kesterite-type nanoparticles, in accordance with the abovemethodology, includes: (a) subjecting a combination of reactioncomponents to conditions conducive to microbially-mediated formation ofthe nanoparticles, wherein the combination of reaction componentsincludes i) anaerobic microbes, ii) a culture medium suitable forsustaining the anaerobic microbes, iii) a chalcophile metal componentthat includes at least one chalcophile metal other than Sn, iv) anon-metal component that includes at least one non-metal selected fromS, Se, and Te, and v) one or more electron donors that provide donatableelectrons to the anaerobic microbes during consumption of the electrondonor by the anaerobic microbes; and (b) isolating the nanoparticles.

In another aspect, the invention is directed to a nanoparticulatesemiconductor composition produced by any of the above methods. In afirst set of embodiments, the nanoparticles have a quantum dotcomposition, such as CdS, ZnS, CdSe, ZnSe, CdTe, or ZnTe. In another setof embodiments, the nanoparticles have a CIGs composition, as describedabove. In yet another set of embodiments, the nanoparticles have akesterite-type of composition, as described above. The nanoparticlesproduced herein possess any one or more of a diverse set of propertiesthat make them useful. Some of the properties particularly consideredherein include photovoltaic, photoluminescent, light-emitting, andthermoelectric properties. Such properties make these nanoparticlesuseful in one or more end applications, e.g., in photovoltaic,light-emitting, and thermoelectric devices.

In particular embodiments, the nanoparticles produced by the abovemethod are crystalline (for example, single-crystalline). Thenanoparticles can have an average size ranging from, for example, about1, 2, 3, 4, or 5 nm to about 10, 20, 50, 100, 150, 200, or 500 nm.

In different embodiments, the nanoparticles possess a photoluminescencepeak characterized by a full-width half maximum (FWHM) value of about,at least, up to, above, or less than 20 nm, 40 nm, 60 nm, 80 nm, 100 nm,150 nm, 200 nm, 250 nm, 300 nm, 350 nm, 400 nm, 450 nm, 500 nm, 600 nm,700 nm, 800 nm, 900 nm, 1,000 nm, 1,100 nm, or 1,200 nm.

The invention advantageously provides a method capable of producing puresemiconductor nanoparticles on a commercial (i.e., bulk) scale at anon-prohibitive cost. A further particular advantage of the method isthat it provides the capability of synthesizing semiconductornanoparticles having selected photoluminescent characteristics over awide range of such characteristics. For example, by controlling thesize, shape, composition, and/or crystalline structure of thenanoparticles, the location or width of the photoluminescence peak canbe accordingly controlled or fine-tuned over a wide range.

Numerous electronic and photonic devices can benefit from such precisecontrol of the photoluminescent properties of semiconductornanoparticles. In particular, photovoltaic devices are currently limitedby the use of photoluminescent materials that are not tunable, orsemi-tunable with great difficulty. Yet, there is a clear and presentneed in the art of photovoltaic devices for photoluminescent-tunablematerials. Other types of devices that can benefit from such tunablematerials include light-emitting and laser diodes. Accordingly, themethod and compositions of the invention can greatly advance severaltypes of devices, including photovoltaic devices.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1. A process diagram illustrating a preferred embodiment of theinvention for preparing metal-chalcogenide crystalline nanoparticles.

FIG. 2. Depiction of a preferred batch-type reactor useful for thedescribed method.

FIG. 3. Depiction of a continuous-type reactor useful for the describedmethod.

FIGS. 4A, 4B. TEM photographs of CdS nanoparticles produced byThermoanaerobacter strain TOR-39 using two different sources of sulfur.

FIGS. 5A-5D. Photoluminescence spectra of CdS nanoparticles producedusing different precursor compounds and microbes: TOR-39 withthiosulfate (FIG. 5A) TOR-39 with sulfite (FIG. 5B), and Desulfovibriosp. G-20 with SO₃ (FIG. 5C), as compared to standard CdS powder (FIG.5D).

FIG. 6. Comparative photoluminescence spectra of CdS nanoparticlesprepared by inorganic synthetic techniques of the prior art.

FIGS. 7A-7D. Comparative X-ray diffraction spectra for sulfide- andselenide-based nanoparticles.

FIGS. 8A, 8B. X-ray diffraction spectra of non-oxide semiconductornanoparticles (i.e., CIGSu) produced according to the instant inventionwith varying stoichiometry.

FIG. 9. Absorption spectra of representativeCu_(x)In_(y)Ga_(1-y)Se_(2±α) (CIGS) and Cu_(x)In_(y)Ga_(1-y)S_(2±α)(CIGSu) nanoparticles.

FIG. 10. X-ray diffraction spectra of Cu₂ZnSnS₄ (Kesterite)nanoparticles produced by TOR-39.

FIGS. 11A-11F. X-ray diffraction spectra of CIGS and CIGSu nanoparticlesproduced by thermophilic, mesophilic, and psychrotolerant bacteria.

DETAILED DESCRIPTION OF THE INVENTION

The non-oxide semiconductor nanoparticles (i.e., “nanoparticles”)produced herein are those containing one or more chalcophile metals in apositive oxidation state, and one or more non-metals selected fromsulfur (S), selenium (Se), tellurium (Te), and arsenic (As), in anegative oxidation state. The chalcophile metal is one, as known in theart, which has a propensity for forming metal-chalcogenide (i.e.,metal-sulfide, metal-selenide, and metal-telluride) compositions. Someexamples of chalcophile metals include, for example, V, Cr, Mn, Fe, Co,Ni, Cu, Zn, Mo, W, Pd, Pt, Au, Ag, Cd, Hg, Ga, In, Tl, Ge, Sn, Pb, Sb,and Bi. Some metals particularly considered herein include Cd, Cu, Fe,Ga, In, Sn, and Zn.

In some embodiments, the nanoparticles have a quantum dot type ofcomposition. Some examples of nanoparticle compositions having a quantumdot composition include CdS, CdSe, CdTe, CdS_(x)Se_(1-x), Cd₃As₂, ZnS,ZnSe, ZnTe, ZnS_(x)Se_(1-x), Zn₃As₂, Ga₂S₃, Ga₂Se₃, Ga₂Te₃, GaAs, In₂S₃,In₂Se₃, In₂Te₃, InAs, CuS, CuSe, CuTe, Cu₃As₂, FeSe, Fe₃As₂, FeAs, PbS,PbSe, PbTe, Pb₃As₂, HgS, HgSe, HgTe, Cd_(x)Zn_(1-x)Te, Cd_(x)Hg_(1-x)Te,Hg_(x)Zn_(1-x)Te, Cd_(x)Zn_(1-x)S, Cd_(x)Zn_(1-x)Se,Cd_(x)Zn_(1-x)S_(y)Se_(1-y), Cd_(x)Hg_(1-x)Se, Hg_(x)Zn_(1-x)Se,Pb_(x)Sn_(1-x)Te, Ga_(x)In_(2-x)Se₃, and Ga_(x)In_(1-x)As, wherein x andy are, independently, an integral or non-integral numerical valuegreater than 0 and less than or equal to 1 (or less than or equal to 2for the expression 2-x).

In other embodiments, the nanoparticles have a composition encompassedby the following general formula:

Cu(In_(x)Ga_(1-x))X₂   (1)

In formula (1) above, x is an integral or non-integral numerical valueof or greater than 0 and less than or equal to 1, and X represents atleast one non-metal selected from S, Se, and Te. In differentembodiments, X represents S, Se, Te, or a combination of two or three ofthese elements. X can also be represented by the formulaS_(j)Se_(k)Te_(m), wherein j, k, and m are independently 0 or anintegral or non-integral numerical value greater than 0 and less than orequal to 1, provided that the sum of j, k, and m is 1. Compositionsaccording to formula (1) and subformulas encompassed therein arecollectively referred to herein as CIGs compositions. The CIGscompositions encompassed by formula (1) may also contain a relativemolar ratio of Cu that diverges from 1.

In particular embodiments, the CIGs composition is according to thefollowing sub-formula:

CuIn_(x)Ga_(1-x)S₂   (1a)

Some specific examples of compositions according to formula (1a) includeCuInS₂, CuIn_(0.9)Ga_(0.1)S₂, CiIn_(0.8)Ga_(0.2)S₂,CuIn_(0.7)Ga_(0.3)S₂, CuIn_(0.6)Ga_(0.4)S₂, CuIn_(0.5)S₂,CuIn_(0.4)Ga_(0.6)S₂, CuIn_(0.3)Ga_(0.7)S₂, CuIn_(0.2)Ga_(0.8)S₂,CuIn_(0.1)Ga_(0.9)S₂, and CuGaS₂.

In other particular embodiments, the CIGs composition is according tothe following sub-formula:

CuIn_(x)Ga_(1-x)Se₂   (1b)

Some specific examples of compositions according to formula (1b) includeCuInSe₂, CuIn_(0.9)Ga_(0.1)Se₂, CuIn_(0.8)Ga_(0.2)Se₂,CuIn_(0.7)Ga_(0.3)Se₂, CuIn_(0.6)Ga_(0.4)Se₂, CuIn_(0.5)Ga_(0.5)Se₂,CuIn_(0.4)Ga_(0.6)Se₂, CuIn_(0.3)Ga_(0.7)Se₂, CuIn_(0.2)Ga_(0.8)Se₂,CuIn_(0.1)Ga_(0.9)Se₂, and CuGaSe₂.

In yet other particular embodiments, the CIGs composition is accordingto the following sub-formula:

CuIn_(x)Ga_(1-x)Te₂   (1c)

Some specific examples of compositions according to formula (1c) includeCuInTe₂, CuIn_(0.9)Ga_(0.1)Te₂, CuIn_(0.8)Ga_(0.2)Te₂,CuIn_(0.7)Ga_(0.3)Te₂, CuIn_(0.6)Ga_(0.4)Te₂, CuIn_(0.5)Ga_(0.5)Te₂,CuIn_(0.4)Ga_(0.6)Te₂, CuIn_(0.3)Ga_(0.7)Te₂, CuIn_(0.2)Ga_(0.8)Te₂,CuIn_(0.1)Ga_(0.9)Te₂, and CuGaTe₂.

In other embodiments, the nanoparticles have a kesterite-typecomposition encompassed by the following general formula:

M₃SnX₄   (2)

In formula (2), M represents at least one chalcophile (typicallydivalent) metal other than Sn, and X is as defined above under formula(1). In particular embodiments, M represents one, two, three, or fourmetals selected from Cu, Fe, Zn, and Cd. In different embodiments, Xrepresents S, Se, Te, or a combination of two or three of theseelements. The relative molar ratio of Sn encompassed by formula (2) maydiverge from 1.

In some embodiments, the kesterite-type compositions of formula (2) areencompassed by the following sub-generic formula:

Cu_(3-x)M′_(x)SnX₄   (2a)

In formula (2a), M′ represents one or more chalcophile metals other thanCu, and X is as defined above. In particular embodiments, M′ representsone, two, or three metals selected from any chalcophile metal, such as,for example, V, Cr, Mn, Co, Ni, Fe, Zn, Cd, Cu, Mo, W, Pd, Pt, Au, Ag,Hg, Ga, In, Tl, Ge, Sn, Pb, Sb, and Bi. Some metals particularlyconsidered herein include Fe, Zn, and Cd. The subscript x is an integralor non-integral numerical value of or greater than 0 and up to or lessthan 1, 2, or 3. In different embodiments, x can be selected to be avalue of precisely or about 1, 2, or 3, or a non-integral value between0 and 3, wherein the term “about” generally indicates within ±0.5, ±0.4,±0.3, ±0.2, or ±0.1 of the value. For example, a value of about 1generically indicates, in its broadest sense, that x can be 0.5 to 1.5(i.e., 1±0.5).

Some particular kesterite-type compositions of formula (2a) areencompassed by the following sub-generic formula:

Cu_(3-x)Zn_(x)SnX₄   (2a-1)

In formula (2a-1), x and X are as described above under formula (2a).Some specific examples of compositions according to formula (2a-1) whenX is S include Cu₃SnS₄ (kuramite), Cu₂ZnSnS₄ (kesterite), CuZn₂SnS₄,Cu_(0.5)Zn_(2.5)SnS₄, Cu_(2.5)Zn_(0.5)SnS₄, Cu_(1.5)Zn_(1.5)SnS₄, andZn₃SnS₄. Other examples of compositions according to formula (2a-1) areprovided by replacing S in the foregoing examples with Se, Te, or acombination of non-metals selected from S, Se, and Te. The relativemolar ratio of Sn encompassed by formula (2a-1) may diverge from 1.

Other particular kesterite-type compositions of formula (2a) areencompassed by the following sub-generic formula:

Cu_(3-x)Fe_(x)SnX₄   (2a-2)

In formula (2a-2), x and X are as described above under formula (2a).Some specific examples of compositions according to formula (2a-2) whenX is S include Cu₃SnS₄, Cu₂FeSnS₄ (stannite), CuFe₂SnS₄,Cu_(0.5)Fe_(2.5)SnS₄, Cu_(2.5)Fe_(0.5)SnS₄, Cu_(1.5)Fe_(1.5)SnS₄, andFe₃SnS₄. Other examples of compositions according to formula (2a-2) areprovided by replacing S in the foregoing examples with Se, Te, or acombination of non-metals selected from S, Se, and Te. The relativemolar ratio of Sn encompassed by formula (2a-2) may diverge from 1.

Other particular kesterite-type compositions of formula (2a) areencompassed by the following sub-generic formula:

Cu_(3-x)Cd_(x)SnX₄   (2a-3)

In formula (2a-3), x and X are as described above under formula (2a).Some specific examples of compositions according to formula (2a-3) whenX is S include Cu₃SnS₄, Cu₂CdSnS₄ (cernyite), CuCd₂SnS₄,Cu_(0.5)Cd_(2.5)SnS₄, Cu_(2.5)Cd_(0.5)SnS₄, Cu_(1.5)Cd_(1.5)SnS₄, andCd₃SnS₄. Other examples of compositions according to formula (2a-3) areprovided by replacing S in the foregoing examples with Se, Te, or acombination of non-metals selected from S, Se, and Te. The relativemolar ratio of Sn encompassed by formula (2a-3) may diverge from 1.

In other embodiments, the kesterite-type compositions of formula (2) areencompassed by the following sub-generic formula:

Cu₂M′_(x)M′_(1-x)SnX₄   (2b)

In formula (2b), each M′ is defined as above under formula (2a), x is anintegral or non-integral numerical value of or greater than 0 and up toor less than 1, and X is as defined above. In particular embodiments,the two M′ metals in formula (2b) are not the same, i.e., the two M′metals in formula (2b) are different. The relative molar ratio of Snencompassed by formula (2b) may diverge from 1, and the relative molarratio of Cu encompassed by formula (2b) may diverge from 2.

Some particular kesterite-type compositions of formula (2b) areencompassed by the following sub-generic formula:

Cu₂Fe_(x)Zn_(1-x)SnX₄   (2b-1)

Some specific examples of compositions according to formula (2b-1) whenX is S include Cu₂Fe_(0.1)Zn_(0.9)SnS₄, Cu₂Fe_(0.2)Zn_(0.8)SnS₄,Cu₂Fe_(0.3)Zn_(0.7)SnS₄Cu₂Fe_(0.4)Zn_(0.6)SnS₄, Cu₂Fe_(0.5)Zn_(0.5)SnS₄,Cu₂Fe_(0.6)Zn_(0.4)SnS₄, Cu₂Fe_(0.7)Zn_(0.3)SnS₄,Cu₂Fe_(0.8)Zn_(0.2)SnS₄, and Cu₂Fe_(0.9)Zn_(0.1)SnS₄. Other examples ofcompositions according to formula (2b-1) are provided by replacing S inthe foregoing examples with Se, Te, or a combination of non-metalsselected from S, Se, and Te. The relative molar ratio of Sn encompassedby formula (2b-1) may diverge from 1, and the relative molar ratio of Cuencompassed by formula (2b-1) may diverge from 2.

In other embodiments, the kesterite-type compositions of formula (2) areencompassed by the following sub-generic formula:

CuM′_(x)M′_(2-x)SnX₄   (2c)

In formula (2c), each M′ is defined as above under formula (2a), x is anintegral or non-integral numerical value of at least or greater than 0and up to or less than 1 or 2, and X is as defined above. In particularembodiments, the two M′ metals in formula (2c) are not the same, i.e.,the two M′ metals in formula (2c) are different. In differentembodiments, x can be selected to be a value of precisely or about 1 or2, or a non-integral value between 0 and 2, wherein the term “about” isas defined under formula (2a). The relative molar ratio of Sn and Cuencompassed by formula (2c) may each diverge from 1.

Some particular kesterite-type compositions of formula (2c) areencompassed by the following sub-generic formula:

CuFe_(x)Zn_(2-x)SnS₄   (2c-1)

Some specific examples of compositions according to formula (2c-1) whenX is S include CuFe_(0.5)Zn_(1.5)SnS₄, CuFeZnSnS₄, andCuFe_(1.5)Zn_(0.5)SnS₄. Other examples of compositions according toformula (2c-1) are provided by replacing S in the foregoing exampleswith Se, Te, or a combination of non-metals selected from S, Se, and Te.The relative molar ratio of Sn and Cu encompassed by formula (2c-1) mayeach diverge from 1.

The semiconductor nanoparticles have a size (i.e., “diameter” forspherical or polyhedral nanoparticles) in the nanoscale regime, i.e.,less than 1 micron (1 μm). In different embodiments, the nanoparticlescan have at least one dimension of at least 1 nm, 2 nm, 3 nm, 4 nm, 5nm, 10 nm, 12 nm, 15 nm, 20 nm, 25 nm, 30 nm, 40 nm, 50 nm, 100 nm, 150nm, 200 nm, 250 nm, 300 nm, 400 nm, or 500 nm, or any range therebetween(e.g., 1-10 nm, 2-10 nm, 1-20 nm, 2-20 nm, 3-20 nm, 1-500 nm, 5-500 nm,1-150 nm, or 5-150 nm), or between any of the foregoing values and up toor less than 1 μm. In one embodiment, the nanoparticles are fairlydisperse in size (e.g., having a size variation of 20%, 30%, 40%, 50%,or greater from a median or mean size). In another embodiment, thenanoparticles are fairly monodisperse in size (e.g., having a sizevariation of or less than 50%, 40%, 30%, 20%, 10%, 5%, 2%, or 1% from amedian or mean size).

The semiconductor nanoparticles can also have any suitable morphology.Some examples of possible nanoparticle shapes include amorphous,fibrous, tubular, cylindrical, rod, needle, spherical, ovoidal,pyramidal, cuboidal, rectangular, dodecahedral, octahedral, plate, andtetrahedral. Often, the semiconductor nanoparticles are equiaxedeuhedral crystals (i.e., typically cubes, octahedra, and modificationsthereof).

The nanoparticles produced by the methodology described herein generallypossess at least one photoluminescence absorption or emission peak. Thepeak can be, for example, in the UV, visible, and/or IR range. Indifferent embodiments, the photoluminescence peak is preferably locatedat, or at least, or above, or less than 200 nm, 250 nm, 300 nm, 320 nm,340 nm, 360 nm, 380 nm, 400 nm, 420 nm, 440 nm, 460 nm, 480 nm, 500 nm,520 nm, 540 nm, 560 nm, 580 nm, 600 nm, 620 nm, 640 nm, 660 nm, 680 nm,700 nm, 720 nm, 740 nm, 760 nm, 780 nm, 800 nm, 820 nm, 840 nm, 860 nm,880 nm, 900 nm, 920 nm, 940 nm, 960 nm, 980 nm, 1000 nm, 1020 nm, 1040nm, 1060 nm, 1080 nm, 1100 nm, 1120 nm, 1140 nm, 1160 nm, 1180 nm, 1200nm, 1220 nm, 1240 nm, 1260 nm, 1280 nm, 1300 nm, 1320 nm, 1340 nm, 1360nm, 1380 nm, 1400 nm, 1420 nm, 1440 nm, 1460 nm, 1480 nm, 1500 nm, 1600nm, 1700 nm, 1800 nm, 1900 nm, 2000 nm, 2500 nm, 3000 nm, 3500 nm, 4000nm, 4500 nm, or 5000 nm, or within ±5 nm, 10 nm, 20 nm, 30 nm, 40 nm, 50nm, 60 nm, 70 nm, 80 mn, 90 nm, or 100 nm of any of these values, orwithin a range bounded by any two of these values (e.g., 400-500 nm or960-980 nm). Some particular ranges considered herein forphotoluminescence peaks include 300-500 nm, 300-1500 nm, 500-1000 nm,500-1500 nm, 435-445 nm, 430-450 nm, 475-525 nm, 1050-1150 nm, 970-980nm, and 970-1000 nm. In particular embodiments, the nanoparticlesdescribed herein exhibit a photoluminescence peak above 500 nm, 800 nm,1000 nm, 1200 nm, or 1500 nm.

In some embodiments, the nanoparticles possess a photoluminescence peakcharacterized by a full-width half maximum (FWHM) value of about or lessthan 20 nanometers (20 nm). In other embodiments, the nanoparticlespossess a photoluminescence peak characterized by a FWHM value of aboutor greater than 20 nm. In different embodiments, the nanoparticlespossess a photoluminescence peak characterized by a FWHM value of aboutor at least, or above, or less than 20 nm, 40 nm, 60 nm, 80 nm, 100 nm,150 nm, 200 nm, 250 nm, 300 nm, 350 nm, 400 nm, 450 nm, 500 nm, 600 nm,700 nm, 800 nm, 900 nm, 1,000 nm, 1,100 nm, and 1,200 nm. In yet otherembodiments, the semiconductor nanoparticles possess a photoluminescencepeak having a FWHM value of about or less than 15 nm, 10 nm, 8 nm, or 5nm.

In a particular aspect, the invention is directed to a method forproducing the semiconductor nanoparticles described above. In themethod, a precursor chalcophile metal component (i.e., one that can formsemiconducting chalcogenide compounds) and a precursor non-metalcomponent (i.e., “non-metal component”) are processed by anaerobicmicrobes in a manner that produces non-oxide semiconductornanoparticles. As the precursor metal and non-metal components arecombined to make the nanoparticle composition, it is understood that,generally, none of the precursor components are equivalent incomposition to the nanoparticle composition. It is contemplated that aprecursor composition could be controlled and tuned to producenanoparticles which have a desired composition or physicalcharacteristic, such as amorphous vs. crystalline, or polycrystallinevs. single-crystalline, or polydispersed (in size) vs. fairlymonodisperse in size.

The precursor metal component contains one or more types of metals inionic form, particularly as described above. The one or more metals aretypically in the form of a salt or coordination compound, or a colloidalhydrous metal oxide or mixed metal oxide, wherein “compound” as usedherein also includes a “material” or “polymer”. Some examples ofprecursor metal compounds applicable herein include the metal halides(e.g., CuCl₂, CdCl₂, ZnCl₂, ZnBr₂, GaCl₃, InCl₃, FeCl₂, FeCl₃, SnCl₂,and SnCl₄), metal nitrates (e.g. Cd(NO₃)₂, Ga(NO₃)₃, In(NO₃)₃, andFe(NO₃)₃), metal perchlorates, metal carbonates (e.g., CdCO₃), metalsulfates (e.g., CdSO₄, FeSO₄, and ZnSO₄), metal oxides (e.g., Fe₂O₃,CdO, Ga₂O₃, In₂O₃, ZnO, SnO, SnO₂), metal hydroxides (e.g., Fe(OH)₃ andZn(OH)₂), metal oxyhydroxides (e.g., FeOOH, or FeO(OH), and theiralternate forms), metal-EDTA complexes, metal amines (e.g., metalalkylamine, piperidine, pyridine, or bipyridine salt complexes), metalcarboxylates (e.g., cadmium acetate), and metal acetylacetonate (i.e.,metal-acac) complexes.

One or more dopant species can be included in the precursor metalcomponent in order to likewise dope the resulting nanoparticles. Thedopant can be any metal or non-metal species, such as any of the metaland non-metal species described above. In some embodiments, the dopantmay be or include one or more lanthanide elements, such as thoseselected from lanthanum (La), cerium (Ce), praseodymium (Pr), neodymium(Nd), samarium (Sm), europium (Eu), gadolinium (Gd), terbium (Tb),dysprosium (Dy), holmium (Ho), erbium (Er), thulium (Tm), ytterbium(Yb), and lutetium (Lu). Generally, the dopant is present in an amountof less than 0.5 molar percent of the resulting nanoparticles, or indifferent embodiments, less than or up to 0.4, 0.3, 0.2, 0.1, 0.05,0.02, or 0.01 molar percent of the resulting nanoparticles. Someexamples of doped compositions include ZnS:Ni, wherein Ni functions as adopant, as described in, for example, Bang et al., Advanced Materials,20:2599-2603 (2008), Zn_(x)Cd_(1-x)S doped compositions, as described inWang et al., Journal of Physical Chemistry C 112:16754-16758 (2008), andZnS:Mn and ZnS:Cu compositions, as described in Song et al., Journal ofPhysics and Chemistry of Solids, 69:153-160 (2008). In otherembodiments, a dopant is excluded, or alternatively, one or more of anyof the generic or specific dopants described above are excluded.

When two or more metals are used as precursors, the molar ratio of metalions can be adjusted such that a particular molar ratio of metals isprovided in the nanoparticle product. Typically, the molar ratio ofmetal ions in the metal component is the molar ratio of metals found inthe nanoparticle product. However, the molar ratio of metals in theproduct may, in several embodiments, differ from the molar ratio ofmetals in the metal component. In a particular embodiment, a desiredmolar ratio of metals is achieved in the nanoparticle product bysuitable adjustment of metal ratios in the precursor metal component.

The total metal concentration should be below a concentration at whichthe metals are toxic to the microbes being used. Typically, the totalmetal concentration is no more than 100 mM. In different embodiments,the total metal concentration may preferably be no more than 90 mM, 80mM, 70 mM, 60 mM, 50 mM, 40 mM, 30 mM, 20 mM, 15 mM, 10 mM, 5 mM, 1 mM,0.5 mM, or 0.1 mM, or within a range resulting from any two of the aboveexemplary values.

The precursor non-metal component provides the resulting nanoparticlecomposition with one or more non-metals selected from S, Se, Te, and As.The non-metal component can include any suitable form of thesenon-metals, including, for example, the elemental or compound forms ofthese non-metals.

In a first embodiment, the non-metal component includes a source ofsulfur. The source of sulfur can be, for example, elemental sulfur (S⁰)or a sulfur-containing compound. In one instance, the sulfur-containingcompound is an inorganic sulfur-containing compound. Some examples ofinorganic sulfur-containing compounds include the inorganic sulfates(e.g., Na₂SO₄, K₂SO₄, MgSO₄, (NH₄)₂SO₄, H₂SO₄, or a metal sulfate), theinorganic sulfites (e.g., Na₂SO₃, H₂SO₃, or (NH₄)₂SO₃), inorganicthiosulfates (e.g., Na₂S₂O₃ or (NH₄)₂S₂O₃), sulfur dioxide,peroxomonosulfate (e.g., Na₂SO₅ or KHSO₅), and peroxodisulfate (e.g.,Na₂S₂O₈, K₂S₂O₈, or (NH₄)₂S₂O₈). In another instance, thesulfur-containing compound is an organosulfur (i.e., organothiol ororganomercaptan) compound. The organosulfur compound contains at leastone hydrocarbon group and is typically characterized by the presence ofat least one sulfur-carbon bond. Some examples of suitable organosulfurcompounds include the hydrocarbon mercaptans (e.g., methanethiol,ethanethiol, propanethiol, butanethiol, thiophenol, ethanedithiol,1,3-propanedithiol, 1,4-butanedithiol, thiophene), thealcohol-containing mercaptans (e.g., 2-mercaptoethanol,3-mercaptopropanol, 4-mercaptophenol, and dithiothreitol), themercapto-amino acids (e.g., cysteine, homocysteine, methionine,thioserine, thiothreonine, and thiotyrosine), mercapto-peptides (e.g.,glutathione), the mercapto-pyrimidines (e.g., 2-thiouracil,6-methyl-2-thiouracil, 4-thiouracil, 2,4-dithiouracil, 2-thiocytosine,5-methyl-2-thiocytosine, 5-fluoro-2-thiocytosine, 2-thiothymine,4-thiothymine, 2,4-dithiothymine, and their nucleoside and nucleotideanalogs), the mercapto-purines (e.g., 6-thioguanine, 8-thioadenine,2-thioxanthine, 6-thioxanthine, 6-thiohypoxanthine, 6-thiopurine, andtheir nucleoside and nucleotide analogs), the thioethers (e.g.,dimethylsulfide, diethylsulfide, diphenylsulfide, biotin), thedisulfides (e.g., cystine, lipoic acid, diphenyl disulfide, irondisulfide, and 2-hydroxyethyldisulfide), the thiocarboxylic acids (e.g.,thioacetic acid), the thioesters, the sulfonium salts (e.g.,trimethylsulfonium or diphenylmethylsulfonium chloride), the sulfoxides(e.g., dimethylsulfoxide), the sulfones (e.g., dimethylsulfone),thioketones, thioamides, thiocyanates, isothiocyanates, thiocarbamates,dithiocarbamates, and trialkylphosphine sulfide (e.g., trioctylphosphinesulfide), thiourea compounds, or any of the inorganic sulfur-containingcompounds, such as those enumerated above, which have been modified byinclusion of a hydrocarbon group. In particular embodiments, theorganosulfur compound includes a sulfur-containing nucleic base (i.e.,S-nucleobase), such as any of the mercapto-pyrimidines andmercapto-purines described above.

In a second embodiment, the non-metal component includes aselenium-containing compound. The source of selenium can be, forexample, elemental selenium (Se⁰) or a selenium-containing compound. Inone instance, the selenium-containing compound is an inorganicselenium-containing compound. Some examples of inorganicselenium-containing compounds include the inorganic selenates (e.g.,Na₂SeO₄, K₂SeO₄, MgSeO₄, (NH₄)₂SeO₄, H₂SeO₄, or a metal selenate), theinorganic selenites (e.g., Na₂SeO₃, H₂SeO₃, or (NH₄)₂SeO₃), inorganicselenosulfates (e.g., Na₂SSeO₃ or (NH₄)₂SSeO₃), selenium dioxide, andselenium disulfide. In another instance, the selenium-containingcompound is an organoselenium compound. The organoselenium compoundcontains at least one hydrocarbon group and is typically characterizedby the presence of at least one selenium-carbon bond. Some examples ofsuitable organoselenium compounds include the hydrocarbon selenols(e.g., methaneselenol, ethaneselenol, n-propaneselenol,isopropaneselenol, and selenophenol (benzeneselenol)), the seleno-aminoacids (e.g., selenocysteine, selenocystine, selenohomocysteine,selenomethionine), the selenopyrimidines (e.g., 2-selenouracil,6-methyl-2-selenouracil, 4-selenouracil, 2,4-diselenouracil,2-selenocytosine, 5-methyl-2-selenocytosine, 5-fluoro-2-selenocytosine,2-selenothymine, 4-selenothymine, 2,4-diselenothymine, and theirnucleoside and nucleotide analogs), the selenopurines (e.g.,6-selenoguanine, 8-selenoadenine, 2-selenoxanthine, 6-selenoxanthine,6-selenohypoxanthine, 6-selenopurine, and their nucleoside andnucleotide analogs), the selenides (e.g., dimethylselenide,diethylselenide, and methylphenylselenide), the diselenides (e.g.,dimethyldiselenide, diethyldiselenide, and diphenyldiselenide), theselenocarboxylic acids (e.g., selenoacetic acid, selenopropionic acid),the selenosulfides (e.g., dimethylselenosulfide), the selenoxides (e.g.,dimethylselenoxide and diphenylselenoxide), the selenones, theselenonium salts (e.g., dimethylethylselenonium chloride), the vinylicselenides, selenopyrylium salts, trialkylphosphine selenide (e.g.,trioctylphosphine selenide, i.e., TOPSe), selenourea compounds, or anyof the inorganic selenium-containing compounds, such as those enumeratedabove, which have been modified by inclusion of a hydrocarbon group. Inparticular embodiments, the organoselenium compound includes aselenium-containing nucleic base (i.e., Se-nucleobase), such as any ofthe selenopyrimidines and selenopurines described above.

In a third embodiment, the non-metal component includes atellurium-containing compound. The source of tellurium can be, forexample, elemental tellurium (Te⁰) or a tellurium-containing compound.In one instance, the tellurium-containing compound is an inorganictellurium-containing compound. Some examples of inorganictellurium-containing compounds include the inorganic tellurates (e.g.,Na₂TeO₄, K₂TeO₄, MgTeO₄, (NH₄)₂TeO₄, H₂TeO₄, H₆TeO₆, or a metaltellurate), the inorganic tellurites (e.g., Na₂TeO₃), and telluriumdioxide. In another instance, the tellurium-containing compound is anorganotellurium compound. The organotellurium compound contains at leastone hydrocarbon group and is typically characterized by the presence ofat least one tellurium-carbon bond. Some examples of suitableorganotellurium compounds include the hydrocarbon tellurols (e.g.,methanetellurol, ethanetellurol, n-propanetellurol, isopropanetellurol,and tellurophenol (benzenetellurol)), the telluro-amino acids (e.g.,tellurocysteine, tellurocystine, tellurohomocysteine,telluromethionine), the telluropyrimidines and their nucleoside andnucleotide analogs (e.g., 2-tellurouracil), the telluropurines and theirnucleoside and nucleotide analogs, the tellurides (e.g.,dimethyltelluride, diethyltelluride, and methylphenyltelluride), theditellurides (e.g., dimethylditelluride, diethylditelluride, anddiphenylditelluride), the telluroxides (e.g., dimethyltelluroxide anddiphenyltelluroxide), the tellurones, the telluronium salts, the vinylictellurides, telluropyrylium salts, tellurourea compounds,24-telluracholestanol, or any of the inorganic tellurium-containingcompounds, such as those enumerated above, which have been modified byinclusion of a hydrocarbon group. In particular embodiments, theorganotellurium compound includes a tellurium-containing nucleic base(i.e., Te-nucleobase), such as any of the telluropyrimidines andtelluropurines described above.

In a fourth embodiment, the non-metal component includes anarsenic-containing compound. In one instance, the arsenic-containingcompound is an inorganic arsenic-containing compound. Some examples ofinorganic arsenic-containing compounds include the inorganic arsenates(e.g., Na₃AsO₄, Na₂HAsO₄, NaH₂AsO₄, H₃AsO₄, Mg₃(AsO₄)₂,1-arseno-3-phosphoglycerate, or a transition metal arsenate), inorganicarsenites (e.g., Na₃AsO₃, Na₂HAsO3, NaH₂AsO₃, H₃AsO₃, Ag₃AsO₃,Mg₃(AsO₃)₂), and arsenic oxides (e.g., As₂O₃ and As₂O₅), and arsenouscarbonate (i.e., As₂(CO₃)₃). In another instance, the arsenic-containingcompound is an organoarsine compound. The organoarsine compound ischaracterized by the presence of at least one hydrocarbon group and atleast one arsenic atom. Some examples of suitable organoarsine compoundsinclude the hydrocarbon arsines (e.g., trimethylarsine, triethylarsine,triphenylarsine, arsole, and 1,2-bis(dimethylarsino)benzene),arsenic-derivatized sugars (e.g., glucose 6-arsenate), arsonic acids(e.g., phenylarsonic acid, 4-aminophenylarsonic acid,4-hydroxy-3-nitrobenzenearsonic acid, 2,3,4-trihydroxybutylarsonic acid,arsonoacetic acid, diphetarsone, diphenylarsinic acid, and3-arsonopyruvate), arseno-amino acids and their derivatives (e.g.,3-arsonoalanine, arsenophenylglycine, and arsenate tyrosine),organoarsine oxides (e.g., methylarsine oxide, 4-aminophenylarsenoxide,oxophenylarsine, and oxophenarsine), 10,10′-oxybis-10H-phenoxarsine,1-arseno-3-phosphoglycerate, arsenobetaine, arsenocholine,arsenotriglutathione, or any of the inorganic arsenic-containingcompounds, such as those enumerated above, which have been modified byinclusion of a hydrocarbon group.

Preferably, the non-metal compound is not a reduced sulfide (e.g., Na₂S,K₂S, H₂S, or (NH₄)₂S), reduced selenide (e.g., H₂Se or (NH₄)₂Se),reduced telluride (e.g., H₂Te or (NH₄)₂Te), or reduced arsenidecompound. As known in the art, such reduced compounds have a propensityfor precipitating various metals from solution. Since direct reaction ofthe non-metal compound and metal to form a precipitate is preferablyavoided in the method, a reduced non-metal compound is preferably usedunder conditions where an adverse reaction or precipitation does notoccur.

The anaerobic microbes considered herein are any microbes known in theart capable of forming semiconductor nanoparticles from one or moretypes of metal ions and one or more non-metals selected from S, Se, Te,and As. The microbe can be, for example, a eukaryotic or procaryotic(and either unicellular or multicellular) type of microbe having thisability. Of particular relevance herein are the procaryotic organisms,which are predominantly unicellular, and are divided into two domains:the bacteria and the archaea. The microbes can be, in addition,fermentative, metal-reducing, dissimilatory, sulfate-reducing,thermophilic, mesophilic, psychrophilic, or psychrotolerant. Themicrobes are preferably those capable of directly reducing (i.e.,without the use of chemical means) a sulfur-containing,selenium-containing, tellurium-containing, or arsenic-containingcompound to, respectively, a sulfide (i.e., S²⁻)-containing, selenide(i.e., Se²⁻)-containing, telluride (i.e., Te²⁻)-containing, or arsenide(i.e., As³⁻)-containing compound, such as H₂S or a salt thereof. In someembodiments, the microbes reduce the sulfur-, selenium-, tellurium-, orarsenic-containing compound without intermediate production of,respectively, elemental sulfur, selenium, tellurium, or arsenic. Inother embodiments, the microbes reduce the sulfur-, selenium-,tellurium-, or arsenic-containing compound with intermediate productionof, respectively, elemental sulfur, selenium, tellurium, or arsenic.

In one embodiment, the microbes considered herein are thermophilic,i.e., those organisms capable of thriving at temperatures of at leastabout 40° C. (and more typically, at least 45° C. or 50° C.) and up toabout 100° C. or higher temperatures. Preferably, the thermophilicmicrobes are either bacteria or archaea, and particularly, thosepossessing an active hydrogenase system linked to high energy electroncarriers.

A group of thermophilic bacteria particularly considered herein are thespecies within the genus Thermoanaerobacter. A particular species ofThermoanaerobacter considered herein is Thermoanaerobacter strainTOR-39, a sample of which was deposited with the American Type CultureCollection (10801 University Blvd., Manassas, Va. 20010) on Sep. 7, 2001as accession number PTA-3695. Strain TOR-39 is a thermophile that growsoptimally at temperatures from about 65 to 80° C. The conditions neededto grow and maintain this strain, including basal medium, nutrients,vitamins, and trace elements are detailed in U.S. Pat. No. 6,444,453,the entire contents of which are incorporated herein by reference. Someparticular strains of Thermoanaerobacter ethanolicus particularlyconsidered herein include T. ethanolicus strain C1 and T. ethanolicusstrain M3.

Another group of thermophilic bacteria particularly considered hereinare the species within the class Thermococci. An order of Thermococciparticularly considered herein is Thermococcales. A family ofThermococcales particularly considered herein is Thermococcaceae. Agenus of Thermococcaceae particularly considered herein is Thermococcus.A species of Thermococcus particularly considered herein is Thermococcuslitoralis.

Another group of thermophilic bacteria particularly considered hereinare the species within the genus Thermoterrabacterium. A species ofThermoterrabacterium particularly considered herein isThermoterrabacterium ferrireducens, and particularly, strain JW/AS-Y7.

Still another group of thermophilic bacteria particularly consideredherein are the species within the phylum Deinococcus-Thermus. A class ofDeinococcus-Thermus particularly considered herein is Deinococci. Anorder of Deinococci particularly considered herein is Thermales. A genusof Thermales particularly considered herein is Thermus. A species ofThermus particularly considered herein is Thermus sp. strain SA-01.

Other thermophilic bacteria particularly considered herein includethermophilic species within any of the genera Thermoanaerobacterium(e.g., T. thermosulfurigenes, T. polysaccharolyticum, T. zeae, T.aciditolerans, and T. aotearoense), Bacillus (e.g., B. infernus),Clostridium (e.g., C. thermocellum), Anaerocellum (e.g., A.thermophilum), Dictyoglomus (e.g., D. thermophilum), andCaldicellulosiruptor (e.g., C. acetigenus, C. hydrothermalis, C.kristjanssonii, C. kronotskiensis, C. lactoaceticus, C. owensensis, andC. saccharolyticus).

In another embodiment, the microbes considered herein are mesophilic(e.g., organisms thriving at moderate temperatures of about 15-40° C.)or psychrophilic (e.g., organisms thriving at less than 15° C.). As usedherein, the term “psychrophilic” also includes “psychrotolerant”.Psychrophilic bacteria are typically found in deep marine sediments, seaice, Antarctic lakes, and tundra permafrost. Some examples of suchmicrobes include species within the genera Shewanella (e.g., S. algastrain PV-1, S. alga, PV-4, S. pealeana, W3-7-1, S. gelidimarina, and S.frigidimarina), Clostridium (e.g., C. frigoris, C. lacusfryxellense, C.bowmanii, C. psychrophilum, C. laramiense, C. estertheticum, and C.schirmacherense), Bacillus (e.g., B. psychrosaccharolyticus, B.insolitus, B. globisporus, B. psychrophilus, B. cereus, B. subtilis, B.circulans, B. pumilus, B. macerans, B. sphaericus, B. badius, B.licheniformis, B. firmus, B. globisporus, and B. marinus), and Geobacter(e.g., G. sulfurreducens, G. bemidjiensis, and G. psychrophilus). Ofparticular interest are those strains capable of anaerobic growth withnitrate as an electron acceptor.

In yet another embodiment, the microbes considered herein aresulfur-reducing (e.g., sulfate- or sulfite-reducing) microbes. In apreferred embodiment, the sulfur-reducing microbes are one or morespecies selected from Desulfovibrio (e.g., D. desulfuricans, D. gigas,D. salixigens, and D. vulgaris), Desulfolobus (e.g., D. sapovorans andD. propionicus), Desulfotomaculum (e.g., D. thermocisternum, D.thermobenzoicum, D. auripigmentum, D. nigrificans, D. orientis, D.acetoxidans, D. reducens, and D. ruminis), Desulfomicrobium (e.g., D.aestuarii, D. hypogeium, and D. salsuginis), Desulfomusa (e.g., D.hansenii), Thermodesulforhabdus (e.g., T. norvegica) the orderDesulfobacterales, and more particularly, the family Desulfobacteraceae,and more particularly, the genera Desulfobacter (e.g., D.hydrogenophilus, D. postgatei, D. giganteus, D. halotolerans, and D.vibrioformis), Desulfobacterium (e.g., D. indolicum, D. anilini, D.autotrophicum, D. catecholicum, D. cetonicum, D. macestii, D. niacini,D. phenolicum, D. vacuolatum), Desulfobacula (e.g., D. toluolica and D.phenolica), Desulfobotulus (D. sapovorans and D. marinus), Desulfocella(e.g., D. halophila), Desulfococcus (e.g., D. multivorans and D.biacutus), Desulfofaba (e.g., D. gelida and D. fastidiosa),Desulfofrigus (e.g., D. oceanense and D. fragile), Desulfonema (e.g., D.limicola, D. ishimotonii, and D. magnum), Desulfosarcina (e.g., D.variabilis, D. cetonica, and D. ovata), Desulfospira (e.g., D.joergensenii), Desulfotalea (e.g., D. psychrophila and D. arctica), andDesulfotignum (D. balticum, D. phosphitoxidans, and D. toluenicum).Several of the sulfur-reducing microbes are either thermophilic ormesophilic. The sulfur-reducing microbes may also be psychrophilic orpsychrotolerant.

In still other embodiments, the microbes considered herein areselenium-reducing (e.g., selenate-, selenite-, or elementalselenium-reducing), tellurium-reducing (e.g., tellurite-, tellurite-, orelemental tellurium-reducing), or arsenic-reducing (e.g., arsenate- orarsenite-reducing). In one embodiment, the selenium-, tellurium-, orarsenic-reducing microbe is one of the sulfur-reducing microbesdescribed above. In another embodiment, the selenium- ortellurium-reducing microbe is selected from other microbes not describedabove, e.g., Thauera selenatis, Sulfospirillum barnesii,Selenihalanerobacter shriftii, Bacillus selenitireducens, Pseudomonasstutzeri, Enterobacter hormaechei, Klebsiella pneumoniae, andRhodobacter sphaeroides. In yet another embodiment, the arsenic-reducingmicrobe is selected from any of the microbes described above, or inparticular, from Sulfurospirillum arsenophilum or Geospirillumarsenophilus. It will also be appreciated that, in addition to theexemplary microorganisms listed above, other types of cultures,including mixed microbial cultures or uncharacterized microbial culturesfrom natural environments, and the like, may also be used in theinvention. For example, cultures not yet characterized from natural hotsprings where various metals are known to be present can demonstratesuitably high metal-reducing or selenium-reducing activity to carry outthe inventive methods even though the exact species or genus of themicrobes may be unknown and more than one species or genus may bepresent in said culture.

The microbes can also be dissimilatory iron-reducing bacteria. Suchbacteria are widely distributed and include some species in at least thefollowing genera: Bacillus, Deferribacter, Desulfuromonas,Desulfuromusa, Ferrimonas, Geobacter, Geospirillum, Geovibrio,Pelobacter, Sulfolobus, Thermoanaerobacter, Thermoanaerobium,Thermoterrabacterium, and Thermus.

The choice of microbe generally involves trade-offs relating to cost,efficiency, and properties of the nanoparticle product. For example,thermophiles may be preferred when more product per unit of time is theprimary consideration, since a high temperature process generallyproduces product at a faster rate. Conversely, psychrophilic orpsychrotolerant microbes may be preferred in a case where one or moreimproved characteristics are of primary consideration, and where theimproved characteristics are afforded to the product by virtue of thecooler process.

The microbes used in the method described herein can be obtained andcultured by any of the methods known in the art. Some of the generalprocesses by which such bacteria may be used are taught in U.S. Pat.Nos. 6,444,453 and 7,060,473, the entire disclosures of which areincorporated herein by reference. The isolation, culturing, andcharacterization of thermophilic bacteria are described in, for example,T. L. Kieft et al., “Dissimilatory Reduction of Fe(III) and OtherElectron Acceptors by a Thermus Isolate,” Appl. and Env. Microbiology,65 (3), pp. 1214-21 (1999). The isolation, culture, and characterizationof several psychrophilic bacteria are described in, for example, J. P.Bowman et al., “Shewanella gelidimarina sp. nov. and Shewanellafrigidimarina sp. nov., Novel Antarctic Species with the Ability toProduce Eicosapentaenoic Acid (20:5ω3) and Grow Anaerobically byDissimilatory Fe(III) Reduction,” Int. J. of Systematic Bacteriology 47(4), pp. 1040-47 (1997). The isolation, culture, and characterization ofmesophilic bacteria are described in, for example, D. R. Lovley et al.,“Geobacter metallireducens gen. nov. sp. nov., a microorganism capableof coupling the complete oxidation of organic compounds to the reductionof iron and other metals,” Arch. Microbiol., 159, pp. 336-44 (1993), thedisclosure of which is incorporated herein by reference in its entirety.

The culture medium for sustaining the microbes can be any of the knownaqueous-based media known in the art useful for this purpose. Theculture medium may also facilitate growth of the microbes. As is wellknown in the art, the culture medium includes such components asnutrients, trace elements, vitamins, and other organic and inorganiccompounds, useful for the sustainment or growth of microbes.

In the method of the invention, the microbes are provided with at leastone electron donor. An electron donor is any compound or materialcapable of being oxidatively consumed by the microbes such thatdonatable electrons are provided to the microbes by the consumptionprocess. The produced electrons are used by the microbes to reduce oneor more non-metal compounds and/or metal ions.

In one embodiment, the electron donor includes one or morecarboxylate-containing compounds that can be oxidatively consumed by themicrobes. Some examples of suitable carboxylate-containing compoundsinclude formate, acetate, propionate, butyrate, oxalate, malonate,succinate, fumarate, glutarate, lactate, pyruvate, glyoxylate,glycolate, and citrate.

In another embodiment, the electron donor includes one or more sugars(i.e., saccharides, disaccharides, oligosaccharides, or polysaccharides)that can be oxidatively consumed by the microbes. Some examples ofsuitable sugars include glucose, fructose, sucrose, galactose, maltose,mannose, arabinose, xylose, lactose, and disaccharides therefrom,oligosaccharides therefrom, or polysaccharides therefrom.

In another embodiment, the electron donor includes one or more inorganicspecies that can be oxidatively consumed by the microbes. The inorganicspecies can be, for example, an oxidizable gas, such as hydrogen ormethane. Such gases can be oxidized by hydrogen-consuming ormethane-consuming microbes which have the capacity to reduce one or moremetals or non-metal compounds by the produced electrons.

The five reaction components described above (i.e., anaerobic microbes,culture medium, metal component, non-metal component, and electron donorcomponent) are combined in a suitable container and subjected toconditions (e.g., temperature, pH, and reaction time) suitable forproducing the nanoparticles from the reaction components. In oneembodiment, the container for holding the reaction components is simpleby containing no more than container walls, a bottom, and a lid. Inanother embodiment, the container is more complex by includingadditional features, such as inlet and outlet elements for gases,liquids, or solids, one or more heating elements, nanoparticleseparation features (e.g., traps or magnets), one or more agitatingelements, fluid recirculating elements, electronic controls forcontrolling one or more of these or other conditions, and so on.

The components may be combined in any suitable manner. For example, eachof the five reaction components or a combination thereof (e.g., theanaerobic microbes and cell culture) may be prepared before thecomponents are combined, or alternatively, obtained in a pre-packagedform before the components are combined. When components or combinationsthereof are provided in package form, the packaged forms may be designedto be used in their entireties, or alternatively, designed such that aportion of each is used (e.g., as aliquots of a concentrate).

In some embodiments, the order of addition of components has essentiallyno bearing on the final compositional and physical characteristics ofthe produced nanoparticles. In other embodiments, the compositionaland/or physical characteristics of the resulting nanoparticles areaffected in some way by the order in which components are combined. Forexample, in some embodiments, it is preferable to first incubate abacterial culture with a non-metal source before introducing the metalsource. The foregoing embodiment is depicted in the flow diagram shownin FIG. 1. In other embodiments, it is preferable to first incubate abacterial culture before introducing the non-metal source and metalsources. In yet other embodiments, it is preferable to incubate abacterial culture in the presence of a both a metal and non-metal sourceat the same time. Typically, the electron donor is included in thebacterial culture medium; however, the electron donor may be addedduring an enrichment step and/or during an incubation step withnon-metal and/or metal.

Also shown in FIG. 1 are some optional steps, such as growing thebacterial culture by incubating the bacteria with only electron donor(enrichment step), and incubating the bacteria with a non-metal sourceand then addition of the metal. The growth step is particularly usefulin culturing a bacterial source to process a metal or non-metal underconditions where the metal or non-metal, at the concentrations used,would be excessively toxic to the bacteria. The growth process, thus,can be particularly useful in producing a bacterial population that canefficiently process an ordinarily toxic species (e.g., selenite,tellurate, arsenate, or a toxic metal species) in order to producenanoparticles therefrom. An incubation step after addition of the metalis generally included when the metal needs to be reduced, such as in theproduction of CIGS nanoparticles wherein, typically, cupric ions arereduced to cuprous ions. Generally, an incubation step is not employedafter addition of the metal when the metal does not require reduction,such as in the case of producing CdS nanoparticles.

In one embodiment, the reaction components are combined immediatelybefore the reaction components are subjected to reaction conditionssuitable for producing semiconductor nanoparticles. This embodiment isparticularly useful for the case when the reaction components react oncontact with each other (i.e., upon being combined) to producenanoparticles.

In another embodiment, at least two of the reaction components aresubstantially unreactive with each other such that they can be in acombined state for a substantial period of time before use withoutsignificant degradation or unwanted reaction. The substantial period oftime is preferably a conventional time of storage (e.g., at least oneweek, one month, three months, six months, or a year). This embodimentcan be beneficial by simplifying the process, specifically, by lesseningthe number of addition steps (i.e., less than five). In a particularembodiment, a solution containing at least three or four of thecomponents is storage-stable under specified conditions (e.g., reducedtemperature). Production of nanoparticles can begin when the remainingone or two components are added, and after the combination is subjectedto conditions conducive to microbially-mediated formation ofsemiconductor nanoparticles. Alternatively, a solution containing all ofthe components is storage-stable. When production of nanoparticles isdesired, the solution is subjected to conditions conducive tomicrobially-mediated formation of semiconductor nanoparticles. Inaddition, storage-stable samples of the reaction components can beprovided in the form of a kit. The samples in the kit can containindividual or combined reaction components.

The method is practiced by subjecting the combined components toconditions that induce the formation of semiconductor nanoparticlestherefrom. Some of the conditions that can affect formation ofsemiconductor nanoparticles from the combined components includetemperature, reaction time, precursor metal concentration, pH, and typeof microbes used. In some embodiments, the reaction conditions may notrequire any special measures other than combining the reactioncomponents at room temperature (e.g., 15-25° C.) and waiting fornanoparticles to grow over a period of time. In other embodiments, thecombined reaction components are, for example, either heated, cooled, ormodified in pH, in order to induce nanoparticle formation.

When thermophilic microbes are used, the temperature at which thereaction is conducted can preferably be at least, for example, 40° C.,45° C., 50° C., 55° C., 60° C., 65° C., 70° C., 75° C., 80° C., 85° C.,or 90° C. depending on the type of thermophilic microbes being used. Anyrange resulting from any two of the foregoing values is alsocontemplated herein. When mesophilic microbes are used, the temperaturecan preferably be at least 15° C., 20° C., 25° C., or 30° C., and up toany of the temperatures given above for thermophilic microbes. Whenpsychrophilic microbes are used, the temperature at which the reactionis conducted can preferably be less than, for example, 40° C., or at orless than 35° C., 30° C., 25° C., 20° C., 15° C., 10° C., 5° C., 0° C.,or −5° C., or any range resulting from any two of the foregoing values.It is to be appreciated that, even though different exemplarytemperatures have been given for each type of microbe, each type ofmicrobe may be capable of thriving in temperatures well outside thetypical temperatures given above. For example, a thermophilic microbemay also be capable of thriving to a useful extent at temperatures below40° C. where mesophilic microbes traditionally thrive; or mesophilic orthermophilic microbes may be capable of thriving to a useful extent attemperatures below 15° C. (i.e., by being psychrotolerant in addition tomesophilic or thermophilic). Particularly when employingThermoanaerobacter sp. strain TOR-39, the temperature is preferablymaintained between about 45° C. and 75° C.

The reaction (incubation) time is the period of time that the combinedreaction components are subjected to reaction conditions necessary forproducing nanoparticles. The reaction time is very much dependent on theother conditions used, as well as the characteristics desired in thenanoparticle product. For example, shorter reaction times (e.g., 1-60minutes) may be used at elevated temperature conditions whereas longerreaction times (e.g., 1-7 days, or 1-3 weeks) may be used at lowertemperatures to obtain a similar yield of product. Typically, shorterreaction times produce smaller particles than particles produced usinglonger reaction times under the same conditions. The incubation may be,for example, between 3 and 30 days, depending on the amount and size ofthe crystalline nanoparticle product desired.

The pH can also be suitably adjusted. Generally, when using thermophilicbacteria, the pH value is preferably within the range of 6.5-9. Forexample, particularly when employing Thermoanaerobacter sp. strainTOR-39, the pH is preferably maintained at a level between about 6.9 and7.5. In different embodiments, depending on the microbe and otherconditions, the pH is preferably acidic by being less than 7 (e.g., a pHof or less than 6.5, 6.0, 5.5, 5.0, 4.5, 4.0, 3.5, 3.0, 2.5, 2.0, 1.5,1.0, or a range resulting from any two of these values), or preferablyalkaline by being above 7 (e.g., a pH of or greater than 7.5, 8.0, 8.5,9.0, 9.5, 10, 10.5, 11, 11.5, or a range resulting from any two of thesevalues), or preferably approximately neutral by having a pH of about 7,e.g., 6.5-7.5.

In addition to selecting reaction conditions (e.g., temperature,reaction time, and pH) on the basis of permitting or inducing theformation of nanoparticles, the reaction conditions can also be selectedfor numerous other purposes, including to modify or optimize the productyield, production efficiency, particle size or size range, particlecomposition or phase (e.g., crystalline vs. semicrystalline vs.amorphous), or particle morphology. For example, lower reactiontemperatures may be employed to provide a more pure orsingle-crystalline product.

Once the nanoparticles are produced, they are isolated (i.e., separated)from the reaction components and byproducts formed by the reactionproducts. Any method known in the art for separation of nanoparticlesfrom reaction components can be used herein.

In one embodiment, nanoparticles are separated from the reactioncomponents by allowing the nanoparticles to settle to the bottom of thecontainer and then decanting the liquid medium or filtering off thenanoparticle product. This settling may be accomplished with or withoutcentrifugation. When centrifugation is used, the centrifugal (i.e., “g”force) causes settling of denser nanoparticles to the bottom or distalend of the spun containers. The collected nanoparticle product may bewashed one or more times to further purify the product. The reactioncontainer may optionally be fitted with a drain valve to allow the solidproduct to be removed without decanting the medium or breaking gasseals.

In another embodiment, the container in which the reaction componentsare housed is attached to (or includes) an external trap from which thenanoparticle product can be removed. The trap is preferably in the formof a recess situated below flowing reaction solution. Nanoparticles inthe flowing reaction solution are denser than the reaction solution, andhence, will settle down into the trap. The flowing reaction solution ispreferably recirculated.

In another embodiment, a filter is used to trap the nanoparticles. Thefilter can be in the form of multiple filters that trap successivelysmaller particles. Depending on the particle size and other variables,one or more filters that trap the nanoparticles may contain a pore sizeof no more than about 0.5, 0.4, 0.3, 0.25, 0.2, 0.1, or 0.05 μm.

In yet another embodiment, in the case where the nanoparticle product ismagnetic, a magnetic source (e.g., electromagnet or other suitablemagnetic field-producing device) can be employed to collect thenanoparticles. The magnetic source can be used as the sole means ofseparation, or used in combination with other separation means, such asa trap or filter.

In a particular set of embodiments, the general method described aboveis specifically directed to the preparation of nanoparticles having aCIGs-type composition according to the general formula (1) describedabove. The method generally includes: (a) subjecting a combination ofreaction components to conditions conducive to microbially-mediatedformation of the nanoparticles, wherein the combination of reactioncomponents includes i) anaerobic microbes, ii) a culture medium suitablefor sustaining the anaerobic microbes, iii) a metal component thatincludes Cu ions and at least one type of metal ion selected from In andGa, iv) a non-metal component that includes at least one non-metalselected from S, Se, and Te, and v) one or more electron donors thatprovide donatable electrons to the anaerobic microbes during consumptionof the electron donor by the anaerobic microbes; and (b) isolating thenanoparticles.

In another particular set of embodiments, the general method describedabove is specifically directed to the production of nanoparticles havinga kesterite-type composition according to the general formula (2)described above. The method generally includes: (a) subjecting acombination of reaction components to conditions conducive tomicrobially-mediated formation of the nanoparticles, wherein thecombination of reaction components includes i) anaerobic microbes, ii) aculture medium suitable for sustaining the anaerobic microbes, iii) achalcophile metal component that includes at least one chalcophile metalother than Sn, iv) a non-metal component that includes at least onenon-metal selected from S, Se, and Te, and v) one or more electrondonors that provide donatable electrons to the anaerobic microbes duringconsumption of the electron donor by the anaerobic microbes; and (b)isolating the nanoparticles.

The method of the invention can be performed in a batchwise manner or ina continuous manner. Examples of suitable arrangements for performingthe method of the invention in a batchwise or continuous manner aredescribed in U.S. Pat. No. 6,444,453, all of which is incorporated byreference herein, and as herein shown in FIGS. 2 and 3, respectively,and as herein described in Examples 7 and 8, respectively. Because thenanoparticles tend to grow larger the longer they remain in the culture,continuous collection of nanoparticle product from a recirculating fluidmay be used as a means of controlling particle size. In addition, thedegree of fluid circulation (e.g., flow rate) can be modulated topromote shedding of the nanoparticles from the microbes.

The method may include one or more chemicals that can facilitatereduction of one or more non-metal compounds or metal ions. However, theproduction of nanoparticles remains microbially-mediated. Therefore,conditions are avoided in which non-metal compounds and/or metal ionsare chemically (i.e., directly) reduced such that semiconductornanoparticles are produced without microbial mediation. Some of theconditions that can affect whether nanoparticle production is direct ormicrobially-mediated includes the absence or presence of a chemicalreductant, the choice of chemical reductant, the processing temperature,and the choice of microbes. The method described herein preferablyexcludes the use of strong reductants because such reductants may havethe ability to directly reduce one or more metal ions or non-metalcompounds before microbial consumption can take place. As used herein, a“strong reductant” is meant to be a chemical stronger in reducing powerthan the known weaker reductants, such as citrate, reducing sugars,alcohols, and hydrogen gas, under standard conditions. Some examples ofchemical reductants preferably excluded from use in the method includethe hydrides (e.g., borohydrides and aluminum hydrides), hydrazines,hypophosphorous acid, and Sn(II) metal salts. It is understood thatweaker reductants, such as the exemplary ones given, may also beunsuitable for the method described herein if conditions are providedthat render these reductants capable of directly reducing non-metalcompounds or metal ions (e.g., by use of temperatures high enough tocause direct reduction as the main reductive process).

In some embodiments, a mediator, such as anthraquinone disulfonic acid(AQDS), is included as an additional component during nanoparticlesynthesis. In other embodiments, mediators are excluded in the method ofthe instant invention. Furthermore, in some embodiments, one or morestabilizing (i.e., surface-active) compounds or materials (e.g.,glutathione, 2-mercaptoethanol, triphenylphosphine, thioglycerol, orother surface-active mercaptan or phosphine compound) is included as anadditional component during nanoparticle synthesis for stabilizing orcontrolling the size of the produced nanoparticles. In anotherembodiment, stabilizing compounds are excluded in the method, wherebythe produced chalcogenide nanoparticles are sufficiently stable in theabsence of a stabilizing compound or material.

Examples have been set forth below for the purpose of illustration andto describe certain specific embodiments of the invention. However, thescope of this invention is not to be in any way limited by the examplesset forth herein.

Example 1 Preparation of ZnS Nanoparticles Using Sulfate-ReducingMicrobes

A mesophilic sulfate-reducing strain Desulfovibrio G-20 was grown in alactate/SO₄ culture medium as taught generally by Li et al., “Reductionof iron oxides enhanced by a sulfate-reducing bacterium and biogenicH₂S”, Geomicrobiol. J., 23:103-117 (2006), the entire disclosure ofwhich is incorporated herein by reference. Zn²⁺ was added as ZnCl₂ at0.2 mM and well-formed highly crystalline ZnS (sphalerite phase)nanoparticles were formed. Precipitated semi-conductor materials wereharvested by repeated centrifugation followed by one or more times ofwashing with deionized water. Particle size was estimated atapproximately 5.9 nm. A similar experimental run using standard mediumcontaining nutrients, vitamins, trace elements, lactate as an electrondonor at 50 mM, and Na₂SO₄ as a non-metal component with 50 mM and withZn²⁺ added as ZnCl₂ at 5 mM yielded ZnS particles estimated atapproximately 3.7 nm in size.

The forgoing example demonstrates that the sulfate-reducing strain G-20was able to make the target ZnS phase in a desirable size range. Theproduct nanoparticles were formed externally to the cells, making iteasy to separate the product without killing the bacteria.Significantly, these nanoparticles were fluorescent, as expected forquantum dots of this size and composition.

Example 2 Preparation of CdS Nanoparticles Using Sulfate-ReducingMicrobes

CdS nanoparticles were synthesized using the same mesophilicsulfate-reducing strain Desulfovibrio G-20. In this case, CdCl₂ as aprecursor metal component was added at 0.06 mM and a sulfur-containingnon-metal compound as 0.06 mM Na₂SO₃ based on CO₃-buffered mediumcontaining nutrients, vitamins, trace elements, and lactate as anelectron donor at 50 mM. Precipitated nanoparticles were harvested byrepeated centrifugation followed by one or more times washing withdeionized water. Well-formed highly crystalline CdS nanoparticles withan extremely sharp photoluminescent peak characterized by a full-widthhalf maximum value of or less than 20 nm, as shown in FIG. 5C, wereformed.

The foregoing example demonstrates that the sulfate-reducing strain G-20was able to make the target CdS phase in the desired size range.Remarkably, the process showed no deleterious toxicity of Cd on thebacteria used. Again, the product nanoparticles were formed externallyto the cells, making it easy to separate the product without killing thebacteria. These nanoparticles had exceptionally good photoluminescence,e.g., exceptionally sharp photoluminescent peaks. The exceptionallysharp photoluminescent peak exhibited by the inventive quantum dotmaterials may arise through one or more factors that have not as yetbeen conclusively identified. Without intending to restrict theinvention in any way or to limit the invention to any particulartheoretical mechanism, it is conjectured that a very sharp (or narrow)photoluminescent peak could be attributed to any of the following: (1)more uniform particle size distribution; (2) more uniformparticle-to-particle chemical composition; (3) more chemical homogeneitywithin each particle; (4) fewer point defects (particularly vacancies);and (5) more uniform particle morphology. Regardless of the exactmechanism(s), it is observed that batches of particles made by theinventive technique exhibit batch properties that are clearly superiorto previously reported quantum dot products.

Example 3 Preparation of ZnS Nanoparticles Using Metal-Reducing Microbes

In an effort to demonstrate the generality of the process, the followingseries of experiments were performed using a metal-reducing strain ofbacteria rather than a sulfate-reducing strain. Fluorescent ZnSnanoparticles were synthesized using the thermophilic metal-reducingstrain TOR-39 cultured in low-NaCl medium for one month. Because TOR-39cannot efficiently reduce sulfate per se, sulfur-containing non-metalcomponent was added in the form of thiosulfate. Zn was added as ZnCl₂.One experiment used 5 mM thiosulfate and 5 mM ZnCl₂, added as sequentialaliquots (1 mM/day). A second experiment used 10 mM thiosulfate and 10mM ZnCl₂, added as sequential aliquots (1 mM/day). The two experimentsproduced highly crystalline ZnS quantum dots with average particle sizesof 6.5 nm and 12 nm, respectively.

This surprising result may be interpreted as follows. Although TOR-39 isa metal-reducing bacterium (e.g., typically reducing Fe³⁺ to Fe²⁺), inthis case the metal was Zn²⁺, which is not microbially reducible.However, the TOR-39 apparently reduced thiosulfate, thereby providingsufficient sulfide to form the desired ZnS phase. As in the previousexamples, the sulfide nanoparticles were produced externally to thecell; they had broad photoluminescent peaks centered at 460 to 480 nm.TOR-39 has other desirable characteristics, notably the fact that it isthermophilic and grows optimally at around 65° C., making the culturefairly insensitive to contamination by bacteria from the environment,most of which would die at this process temperature.

Example 4 Preparation of CdS Nanoparticles Using Metal-Reducing Microbes

CdS nanoparticles were synthesized using the same thermophilicmetal-reducing strain TOR-39 as in the previous example, using amodified TOR-39 medium (without bicarbonate buffer and mineralsolution). Applicants have found that using NaHCO₃ buffer caused theprecipitation of Cd carbonate (otavite), so buffering with NaOH and MOPSis preferred. Recognizing that TOR-39 cannot reduce sulfate, severalsulfur-containing non-metal sources were used as shown in the followingtable.

Table Showing CdS Production by TOR-39 Using Different Sulfur Substrates

TEM S source Concentration Cd concentration Precipitates^(a) imagescysteine-S 0.5 mL/day 5 ppm/day Haw cysteine-S 0.5 mL/day 5 ppm/day HawFIG. 4B thiosulfate 10 mM 5 ppm/day Haw + Gre FIG. 4A sulfite 10 mM 5ppm/day Haw + Gre thiosulfate 10 mM 30 ppm/day Haw + Gre thiosulfate 10mM 100 ppm/day Haw + Gre ^(a)Haw = hawleyite and Gre = greenockite

The above series of experiments demonstrates, surprisingly, thatfermentative strain TOR-39 can produce CdS quantum dots using a numberof sulfur sources, and furthermore, did not suffer any adverse effectsfrom Cd concentrations up to 100 ppm per day. The quantum dots producedin these runs showed superior photoluminescence. For example, samplesmade using cysteine-S at 0.5 mL and Cd at 5 ppm/day showed a sharpphotoluminescent peak at ˜440 nm and broader photoluminescence at ˜550nm. Another sample prepared using thiosulfate at 10 mM and Cd at 5ppm/day showed a photoluminescent peak at ˜440 nm with a FWHM of about10 nm, as shown in FIG. 5A. This value represents a nearly three-foldimprovement over conventionally-prepared materials, as further discussedbelow and as shown by FIG. 6.

Example 5 Preparation of Nanoparticles of CIGSu CompositionCuIn_(0.5)Ga_(0.5)S₂

A series of experiments were run to synthesize particles having thenominal composition CuIn_(0.5)Ga_(0.5)S₂. Cultures of Thermoanaerobactersp. strain TOR-39 were cultured in “FeS medium”, which is based on thestandard TOR-39 culture medium as taught, for example, in U.S. Pat. No.6,444,453, modified by omitting NaHCO₃ buffer, and includingapproximately 15 mM MOPS (i.e., 3-(N-morpholino)propanesulfonic acidsodium salt or 4-morpholinepropanesulfonic acid sodium salt). MOPS at a1.5 M stock solution was titrated to pH˜8.0 with 10 N NaOH and added tothe culture medium at a final concentration of ˜15 mM to preventcarbonate formation, at 65° C. for three weeks. The electron donor was10 mM glucose. Thiosulfate concentration was 10 mM. Metal stock solutionconsisted of cupric or cuprous chloride, indium chloride, and galliumchloride in molar ratios of 2:1:1, so that a 0.2 M stock solution has0.2, 0.1, and 0.1 M Cu, In, and Ga, respectively. Metals were typicallyadded at the rate of 0.2 mM (copper basis) per day in order to avoidtoxicity to the bacteria.

As shown by FIG. 7A, X-ray diffraction results confirmed that controlsamples (i.e., without microbes) did not produce the desired CIGSu phaseor the ternary end-members CuInS₂ or CuGaS₂. However, as shown in FIG.7B, well-defined diffraction lines were observed in the batchescontaining TOR-39, corresponding to the (112), (204), and (312)reflections of CuIn_(0.5)Ga_(0.5)S₂ fitting between end-members ofCuGaS₂ and CuInS₂, and exhibiting a linear relationship of diffractionangle (20) following Vegard's Law. The crystallite size was estimated tobe about 3 nm. It was also observed that using a cupric source produceda higher yield than using a cuprous source (i.e., CuCl), and that yieldsas high as 300 mg per liter of medium could be obtained.

Based on the foregoing results, the skilled artisan will appreciate thatsubstitutions of other metals (or modifications of the In:Ga ratio) maybe carried out by routine experimentation. Similarly, substitution withselenium or tellurium can be used to synthesize analogous selenide ortelluride particles.

Example 6 Preparation of Nanoparticles of CIGS CompositionCuIn_(0.5)Ga_(0.5)Se₂

A series of experiments were run to synthesize particles having thenominal composition CuIn_(0.3)Ga_(0.7)Se₂. Cultures ofThermoanaerobacter sp. strain M1 were cultured in “FeS medium”, which isbased on the standard TOR-39 culture medium as taught, e.g., in U.S.Pat. No. 6,444,453 but with 15 mM MOPS buffer as described above. Theelectron donor was 10 mM glucose. Sodium selenite concentration was 5mM. Metal stock solution consisted of cupric chloride, indium chloride,and gallium chloride in molar ratios of 2:1:1, so that a 0.2 M stocksolution has 0.2, 0.1, and 0.1 M Cu, In, and Ga, respectively. Theenriched culture, including the electron donor and M1, was dosed withsodium selenite as a non-metal component and then several minutes tohours later the culture was additionally dosed with a solutioncontaining metal component. Metals were typically added at the rate of0.25 mM (copper basis) per day in order to avoid toxicity to thebacteria.

Precipitated nanoparticles were harvested by repeated centrifugationfollowed by one or more times washing with deionized water withoutlysing, then freeze-dried for further phase identification using XRD. Asshown by FIG. 7C, X-ray diffraction results confirmed that controlsamples (i.e., without microbes) did not produce the desired CIGS phase.However, as shown by FIG. 7D, well-defined diffraction linescorresponding to the (112), (220), and (312) reflections ofCuIn_(0.3)Ga_(0.7)Se₂were observed in the microbial batches. In anotherexperiment utilizing an uncharacterized thermophilic anaerobic culturegrowing at 65° C., ten discrete fractional additions of metals wereadded over a period of fourteen days. After a total of three weeks ofincubation the culture produced CuIn_(0.3)Ga_(0.7)Se₂ which exhibitedclear XRD peaks.

Based on the foregoing results, the skilled artisan will appreciate thatsubstitutions of other metals (or modifications of the In:Ga ratio) andthe reduction of secondary phases may be carried out through routineexperimentation.

Example 7 A Batch-Type Bioprocessing Reactor

FIG. 2 is a simplified diagram of a batch-type bioprocessing reactor 30suitable for carrying out the inventive process shown in FIG. 1. Thereactor includes a container 32 constructed of glass or other inertmaterial. A culture medium 34 is introduced in the container 32. Theculture medium 34 contains an aqueous solution of nutrients, traceelements, vitamins, and other organic and inorganic compounds asdescribed in the foregoing examples. The solutions described above areprovided for illustrative purposes. Other solution constructs arepossible, depending on the specific implementation.

The container 32 is sealed to prevent the entry of air into theheadspace gas region 36, thereby maintaining anaerobic conditions withinthe culture as well as permitting the inventive process to be carriedout at pressures greater or less than ambient if desired. A gas conduit38 is preferably included to allow the introduction of selected gasesinto the container and to allow gases to exit the container. A heatingelement 40 is preferably provided proximate to the container 32 tomaintain the culture medium 34 at a desired temperature for growth ofthe anaerobic thermophilic bacteria. An electron donor is introducedinto the culture (e.g., as a gas, such as hydrogen or CO) through thegas conduit 38, or dissolved directly into the culture medium 34 in thecase of simple organics, such as glucose, lactate, and pyruvate. Anelectron acceptor (i.e., non-metal component) is provided in the form ofone or more reducible species of S, Se, Te, or As, preferably dissolvedor suspended in the culture medium 34. A source of a desired transitionmetal, preferably a chalcophile element such as Zn, Cd, Hg, Ga, In, Ag,W, Fe, Co, Cu, Ni, etc., is provided as either a soluble species or asuspended particulate. One or more additional dopant species, which mayor may not be reducible, may be provided in the culture medium 34. Thedopant species may be a metal, such as a small amount of Ag added insubstitution for some of the Zn in ZnS (i.e., a ZnS:Ag dopedcomposition), or Hg added in substitution for Cd in CdTe. Alternatively,substitutions may be made in the nonmetal, such as replacing some of theS with Se and/or Te. Thus, the skilled artisan may vary thecharacteristics of the product over a wide range by selection of avariety of different dopants in a variety of different concentrations ormolar ratios.

A crystalline product 42 forms in the container 32 as the bacteriareduces the reducible species. When a sufficient quantity of crystallineproduct 42 has been produced and allowed to settle to the bottom of thecontainer 32, the culture medium 34 is preferably decanted and thecrystalline product 42 collected and washed. The incubation may bebetween 3 and 30 days, depending on the amount and size of thecrystalline product desired.

Example 8 A Continuous-Type Bioprocessing Reactor

The disclosed process may also be performed in a continuous arrangementas shown schematically by the bioreactor 50 shown in FIG. 3. Thebioreactor 50 operates in a similar manner as the bioreactor 30 of FIG.2. The bioreactor 50 preferably includes a fluid recirculator 52 thatallows the culture medium 34 to pass through an external trap 54 fromwhich the crystalline product 42 can be removed. The trap 54 mayseparate the crystalline product 42 from the circulating culture mediumby settling, due to the greater density of the crystalline product 42.Continuous collection of product from the circulating fluid may also beused as a means of controlling particle size, because the particles tendto grow larger the longer they remain in the culture.

An additional fluid valve 58 may be provided through which additionalculture medium or nutrients 34 may be added from an external reservoir60 while maintaining the anaerobic conditions within the container 32.Furthermore, because the photoluminescence of quantum dots is generallya function of their size and composition, a source of UV light and aspectrophotometer may be provided to periodically or continuouslyanalyze the circulating fluid so that product may be extracted when thephotoluminescent values reach the desired values.

The composition of the culture medium 34 may be changed periodically inorder to make crystalline products 42 of various selected compositions.The electron acceptor may be adjusted during the process, to make, forexample, particles with a compositionally zoned or layered structure forspecial applications.

Example 9 TEM and XRD Analysis of CdS Quantum Dots

FIG. 4 shows TEM photographs of exemplary CdS quantum dots formed inaccordance with the present invention at a temperature of about 65° C.The particles clearly exhibit substantially equiaxed, euhedralcrystallite morphology. The upper photo shows particles produced byTOR-39 using thiosulfate as the source of sulfur. XRD measurementsdetermined that two predominant crystalline phases are cubic CdS(hawleyite) and hexagonal CdS (greenockite). The lower photo showsparticles produced by TOR-39 using cysteine-S as the source of sulfur.XRD measurements indicate that the predominant crystalline phase iscubic CdS (hawleyite). This surprising result indicates not only thatnanometer-sized particles can be synthesized by fermentative bacteria,but also that the choice of sulfur source can influence the particularcrystalline phase when a compound can exist in more than one polymorph.

Example 10 Photoluminescence Analysis of CdS Quantum Dots

Optical photoluminescence data collected on several batches of particlesmade according to embodiments of the instant invention are presented inFIG. 5, wherein it can be seen that the microbially-produced materialsexhibit very sharp photoluminescence, with peaks having a FWHM around 10nm. FIGS. 5A and 5B show almost identical emission spectra of CdSquantum dots produced by TOR-39 using different sulfur sources,thiosulfate and sulfite, respectively. FIG. 5C shows emission spectrumof nanoparticles produced by G-20 exhibiting a tail toward longerwavelength, which may have been caused by minor impurities in the XRDpattern (data not shown). By comparison, FIG. 5D shows thephotoluminescence spectrum for standard CdS powder having a particlesize in the micron range. As shown, the standard CdS powder exhibits anextremely broad and poorly defined photoluminescence spectrum ascompared to the CdS nanoparticles produced according to the presentinvention.

For further comparison, CdS quantum dots prepared inorganically bycurrent state of the art methods (see, for example, Darugar et al.,“Observation of optical gain in solutions of CdS quantum dots at roomtemperature in the blue region”, Appl. Phys. Lett. 88: 261108 (2006)exhibited photoluminescence peaks (as shown in FIG. 6) that were notnearly as sharp as those of the present invention (e.g., FWHM=28 nm).Accordingly, a roughly three-fold improvement has been provided by usingthe bacterially-mediated process of the invention.

It will be appreciated that process variables such as choice of electrondonor and incubation time may be controlled to adjust the averagecrystallite size. Adjusting the crystallite size (and particularly thesize distribution in a particular batch) will generally influence theobserved photoluminescent behavior, and particularly, the sharpness ofthe PL peak. In particular, without being bound by any theory, it isbelieved that the sharpness of the PL peak of the nanoparticlecompositions of the present invention can be attributed to either theincreased size uniformity (i.e., monodispersity) or the increaseduniformity in composition or crystalline morphology of the nanoparticlesas compared to nanoparticle compositions of the art.

Example 11 Tunable Stoichiometry of Non-Oxide SemiconductorNanoparticles

The conditions used in the bacterial-mediated process of the inventioncan advantageously be adjusted in order to adjust, tune, or optimize thecompositional or physical characteristics of the produced nanoparticles.For example, X-ray diffraction results confirmed that compositions ofvarious stoichiometries within the formulas Cu_(x)In_(y)Ga_(1-y)Se_(2±α)(CIGS) and Cu_(x)In_(y)Ga_(1-y)S_(2±α) (CIGSu) can be produced by usingthe bacterially-mediated process of the invention. In particular, whenx=1 and α=0, the stoichiometry of single phase CIGSu was reproduciblytuned based on the mole fraction of the metal-compounds, i.e., as y ischanged from 0 to 1, the endpoints of which correspond to theend-members CuGaS₂ and CuInS₂, respectively. For example, theoretically,metal precursors of nominal composition CuIn_(0.3)Ga_(0.7)S₂,CuIn_(0.4)Ga_(0.6)S₂, CuIn_(0.5)Ga_(0.5)S₂, and CuIn_(0.6)Ga_(0.4)S₂have 0.7, 0.6, 0.5, and 0.4 Ga/(Ga+In) molar ratios, respectively. Theobserved Ga/(Ga+In) ratios, as obtained using ICP-MS, revealed 0.45,0.39, 0.31, and 0.24, respectively, showing good correlation coefficient(R²=0.995). A discrepancy can arise from various factors, for example,the different hydrolysis constant of each metal in the aqueous system,supplied anion species (i.e., sulfur or selenium), and reducing kineticsof non-metal components.

As shown in FIG. 8A, Thermoanaerobacter strain TOR-39 culture producedCuIn_(0.2)Ga_(0.8)S₂, CuIn_(0.3)Ga_(0.7)S₂, CuIn_(0.4)Ga_(0.6)S₂,CuIn_(0.5)Ga_(0.5)S₂, and CuIn_(0.6)Ga_(0.4)S₂ (FIG. 8A), as x, y, and αwere varied. As shown in FIG. 8B, tunability in stoichiometry was alsodemonstrated by use of Desulfovibrio strain G-20, by which the same orsimilar compositions of various stoichiometries were produced.

Example 12 Absorption Spectra of CIGS and CIGSu

Significantly, absorption and/or emission characteristics of CIGS andCIGSu nanoparticles produced by the methodology described herein can beadjusted by corresponding adjustment in the percent atomic compositionof elements, such as Ga, In, S, Se, and Cu. By such adjustment, thebandgap of CIGS and CIGSu nanoparticles can be tuned from 1.0 eV to 2.4eV, the key bandgap range for photovoltaics (see, for example, Banger etal., “Single source precursor for thin film solar cells”,NASA/TM-2002-211496). As shown by FIG. 9, the bandgaps ofCuIn_(0.3)Ga_(0.7)Se₂ and CuIn_(0.5)Ga_(0.5)S₂ produced in accordancewith the methodology described herein were 1.82 eV and 2.1 eV,respectively.

Example 13 Preparation of Nanoparticles of Composition of Cu₂ZnSnS₄(Kesterite)

A series of experiments were performed to synthesize particles havingthe nominal composition Cu₂ZnSnS₄. Cultures of Thermoanaerobacter sp.strain TOR-39 were cultured in “FeS medium”, which is based on thestandard TOR-39 culture medium as taught, for example, in U.S. Pat. No.6,444,453, modified by omitting NaHCO₃ buffer, and includingapproximately 15 mM MOPS (i.e., 3-(N-morpholino)propanesulfonic acidsodium salt or 4-morpholinepropanesulfonic acid sodium salt). MOPS at a1.5 M stock solution was titrated to pH˜8.0 with 10 N NaOH and added tothe culture medium at a final concentration of ˜15 mM to preventcarbonate formation, at 65° C. for three weeks. The electron donor was10 mM glucose. Thiosulfate concentration was 10 mM. The metal stocksolution consisted of cupric chloride, zinc chloride, and stannouschloride in molar ratios of 2:1:1, so that a 0.2 M stock solution has0.2, 0.1, and 0.1 M Cu, Zn, and Sn, respectively. Metals were typicallyadded at the rate of 0.2 mM (copper basis) per day in order to avoidtoxicity to the bacteria. The incubated culture containing electrondonor, TOR-39, and thiosulfate as a nonmetal component was dosed by thestock solution containing the metal component.

As shown by FIG. 10, X-ray diffraction results confirmed thatwell-defined diffraction lines were observed in the batches containingTOR-39, corresponding to the (112), (220), and (312) reflections ofnominal Cu₂ZnSnS₄. It was further discovered that use of an impactdosing (which doses the total concentration at one time compared topulsed dosing) also produced a kesterite phase. The foregoingobservation indicates that there was little toxicity from Cu, Zn, andSn, thus allowing microbial activity. This is in contrast to the greatertoxicity found using Cu, In, and Ga during the formation of CIGs.

Based on the foregoing results, the skilled artisan will appreciate thatsubstitutions of other metals, or adjustment of Cu, Zn, and Sn ratios,may be employed by routine experimentation to produce other relatedcompositions useful in photovoltaics. In particular, substitution of Sfor Se or Te, or combining S with Se and/or Te can produce other relatedand useful nanoparticles for photovoltaics.

Example 14 Non-Oxide Semiconductor Nanoparticles Produced by VariousMicrobes

FIG. 11 shows the X-ray diffraction (XRD) spectra of several CIGS andCIGSu nanoparticles produced in accordance with the methodology of theinstant invention. The XRD spectra show that the methodology describedherein is capable of producing non-oxide semiconductor nanomaterialsusing various microbes. For example, the top XRD pattern is forCuIn_(0.2)Ga_(0.8)Se₂ as produced by Thermoanaerobacter (TOR-39), whilethe second from the top XRD pattern is for CuIn_(0.3)Ga_(0.7)Se₂ asproduced by T. ethanolicus (M1). The middle two XRD patterns showCuIn_(0.3)Ga_(0.7)Se₂ produced by thermophilic enrichments (OB), as wellas CuIn_(0.3)Ga_(0.7)Se₂ produced by a separate thermophilic enrichmentculture designated WC. The bottom two XRD patterns are forCuIn_(0.6)Ga_(0.4)S₂, as produced by Desulfovibrio desulfuricans (G-20),and CuIn_(0.3)Ga_(0.7)S₂, as produced by Shewanella algae (BrY). All ofthese nanoparticles show the characteristic XRD peaks expected for theindicated compositions, although the peaks in some of the XRD spectraare more pronounced or sharper than in others in that a higher ratio ofpeak height over full-width half maximum is evidenced. Higher ratios ofpeak height over full-width half maximum are generally indicative of ahigher degree of crystallinity. Furthermore, higher degrees of crystalstructure order were found to generally correlate with higher purity andmore uniform composition.

The thermophilic enrichment culture OB was obtained from sedimentsaround the edges of Obsidian Pool in Yellowstone National Park (YNP).Temperatures at the discrete sample locations ranged from 58-75° C.Enrichment culture WC was derived from discrete samples of multiple hotsprings along the flow path of White Creek of YNP. Temperatures of thediscrete sample locations were greater than 55° C.

As indicated by FIG. 11, it has surprisingly been found thatnanoparticles produced by thermophiles (i.e., Thermoanaerobacter, FIGS.11A to D) tend to exhibit a higher degree of crystallinity compared tonanoparticles produced by mesophilic (i.e., Desulfovibrio, FIG. 11E) andpsychrotolerant (i.e., Shewanella, FIG. 11F) bacteria. The foregoingobservations imply that, at least under some conditions, highertemperatures may facilitate crystal growth and/or enhance thecrystallinity characteristics of the nanoparticles.

While there have been shown and described what are at present consideredthe preferred embodiments of the invention, those skilled in the art maymake various changes and modifications which remain within the scope ofthe invention defined by the appended claims.

1. A method for producing non-oxide semiconductor nanoparticles, themethod comprising: (a) subjecting a combination of reaction componentsto conditions conducive to microbially-mediated formation of non-oxidesemiconductor nanoparticles, wherein said combination of reactioncomponents comprises i) anaerobic microbes, ii) a culture mediumsuitable for sustaining said anaerobic microbes, iii) a chalcophilemetal component comprising at least one type of metal ion, iv) anon-metal component comprising at least one non-metal selected from thegroup consisting of S, Se, Te, and As, and v) one or more electrondonors that provide donatable electrons to said anaerobic microbesduring consumption of the electron donor by said anaerobic microbes; and(b) isolating said non-oxide semiconductor nanoparticles comprised of atleast one of said metal ions and at least one of said non-metals.
 2. Themethod of claim 1, wherein said metal component comprises one or moremetals selected from V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Mo, W, Pd, Pt, Au,Ag, Cd, Hg, Ga, In, Tl, Ge, Sn, Pb, Sb, and Bi.
 3. The method of claim1, wherein said metal component comprises one or more metals selectedfrom Cd, Cu, Fe, Ga, In, Sn, and Zn.
 4. The method of claim 1, whereinsaid non-metal component is a reducible sulfur-containing,selenium-containing, tellurium-containing, or arsenic-containingcomponent.
 5. The method of claim 4, wherein said reduciblesulfur-containing component comprises sulfate, sulfite, elementalsulfur, or thiosulfate.
 6. The method of claim 4, wherein said reducibleselenium-containing component comprises selenate, selenite, elementalselenium, or selenosulfate.
 7. The method of claim 4, wherein saidreducible tellurium-containing component comprises tellurate, tellurite,or elemental tellurium.
 8. The method of claim 4, wherein said reduciblearsenic-containing compound is an arsenate or arsenite compound.
 9. Themethod of claim 4, wherein said non-metal component comprises asulfur-containing, selenium-containing, or tellurium-containing aminoacid or nucleic base.
 10. The method of claim 1 wherein said one or moreelectron donors include one or more carboxylate-containing compoundsthat can be oxidatively consumed by the microbes.
 11. The method ofclaim 1 wherein said one or more electron donors include one or moresugar compounds that can be oxidatively consumed by the microbes. 12.The method of claim 1 wherein said one or more electron donors includeone or more oxidizable gaseous compounds or elements that can beoxidatively consumed by the microbes.
 13. The method of claim 1 whereinthe non-oxide semiconductor nanoparticles possess a size within a rangeof about 1 nm to about 500 nm.
 14. The method of claim 1 wherein thenon-oxide semiconductor nanoparticles possess a size within a range ofabout 1 nm to about 200 nm.
 15. The method of claim 1 wherein thenon-oxide semiconductor nanoparticles possess a size within a range ofabout 1 nm to about 100 nm.
 16. The method of claim 1 wherein thenon-oxide semiconductor nanoparticles possess a size within a range ofabout 1 nm to about 20 nm.
 17. The method of claim 1 wherein thenon-oxide semiconductor nanoparticles possess a size within a range ofabout 1 nm to about 10 nm.
 18. The method of claim 1, wherein saidanaerobic microbes are thermophilic, and said method is conducted at atemperature of at least 40° C.
 19. The method of claim 1, wherein saidanaerobic microbes are mesophilic or psychrotolerant, and said method isconducted at a temperature of less than 40° C.
 20. The method of claim1, wherein said anaerobic microbes are sulfate-reducing microbes. 21.The method of claim 1, wherein said anaerobic microbes aremetal-reducing microbes.
 22. The method of claim 1, wherein the methodis conducted under substantially anaerobic conditions.
 23. Ananoparticulate semiconductor composition comprising crystallinenanoparticles having an average size ranging from about 1 to about 500nm, said crystalline nanoparticles comprising one or more metals and oneor more non-metals selected from S, Se, Te, and As, wherein saidcrystalline nanoparticles exhibit a photoluminescence peak characterizedby a full-width half maximum value of less than 20 nm.
 24. Thecomposition of claim 23 further characterized by having at least onephotoluminescent peak in the range of 300 to 500 nm.
 25. The compositionof claim 23 further characterized by having at least onephotoluminescent peak above 500 nm.
 26. The composition of claim 23,wherein said one or more metals are selected from Cd, Cu, Fe, Ga, In,Sn, and Zn.
 27. The method of claim 1, wherein said non-metal componentis comprised of one or more inorganic substances selected fromsulfur-containing, selenium-containing, tellurium-containing, andarsenic-containing substances.
 28. The method of claim 1, wherein saidnon-metal component is comprised of one or more organic compoundsselected from organsulfur, organoselenium, organotellurium, andorganoarsine compounds.
 29. The method of claim 1, wherein saidnon-oxide semiconductor nanoparticles exhibit a photoluminescence peakcharacterized by a full-width half maximum value of less than 20 nm. 30.A method for producing nanoparticles having a composition according tothe formula:Cu(In_(x)Ga_(1-x))X₂   (1) wherein x is an integral or non-integralnumerical value of or greater than 0 and less than or equal to 1, and Xrepresents at least one non-metal selected from S, Se, and Te; themethod comprising: (a) subjecting a combination of reaction componentsto conditions conducive to microbially-mediated formation of saidnanoparticles, wherein said combination of reaction components comprisesi) anaerobic microbes, ii) a culture medium suitable for sustaining saidanaerobic microbes, iii) a metal component comprising Cu ions and atleast one type of metal ion selected from In and Ga, iv) a non-metalcomponent comprising at least one non-metal selected from S, Se, and Te,and v) one or more electron donors that provide donatable electrons tosaid anaerobic microbes during consumption of the electron donor by saidanaerobic microbes; and (b) isolating said nanoparticles.
 31. The methodof claim 30, wherein said non-metal component is comprised of one ormore inorganic substances selected from sulfur-containing,selenium-containing, and tellurium-containing inorganic substances. 32.The method of claim 30, wherein said non-metal component is comprised ofat least one organic compound selected from organsulfur, organoselenium,and organotellurium compounds.
 33. The method of claim 32, wherein saidat least one organic compound is selected from sulfur-containing,selenium-containing, and tellurium-containing amino acids and nucleicbases.
 34. The method of claim 30, wherein said nanoparticles exhibit atleast one photoluminescent peak between 400 nm and 1500 nm.
 35. A methodfor producing nanoparticles having a kesterite-type compositionaccording to the formula:M₃SnX₄   (2) wherein M represents at least one chalcophile metal otherthan Sn, and X represents at least one non-metal selected from S, Se,and Te; the method comprising: (a) subjecting a combination of reactioncomponents to conditions conducive to microbially-mediated formation ofsaid nanoparticles, wherein said combination of reaction componentscomprises i) anaerobic microbes, ii) a culture medium suitable forsustaining said anaerobic microbes, iii) a chalcophile metal componentcomprising at least one chalcophile metal other than Sn, iv) a non-metalcomponent comprising at least one non-metal selected from S, Se, and Te,and v) one or more electron donors that provide donatable electrons tosaid anaerobic microbes during consumption of the electron donor by saidanaerobic microbes; and (b) isolating said nanoparticles.
 36. The methodof claim 35, wherein said chalcophile metal component comprises one ormore metals selected from Cu, Fe, Zn, and Cd.
 37. The method of claim35, wherein said non-metal component is comprised of one or moreinorganic substances selected from sulfur-containing,selenium-containing, and tellurium-containing inorganic substances. 38.The method of claim 35, wherein said non-metal component is comprised ofat least one organic compound selected from organsulfur, organoselenium,and organotellurium compounds.
 39. The method of claim 38, wherein saidat least one organic compound is selected from sulfur-containing,selenium-containing, and tellurium-containing amino acids and nucleicbases.
 40. The method of claim 35, wherein said nanoparticles exhibit atleast one photoluminescent peak between 400 nm and 1500 nm.
 41. Themethod of claim 1, wherein steps (a) and (b) are performed as a singlestep process.